System and method for measurement of material property using variable reflector

ABSTRACT

A system and method for measuring a material includes at least one transmitter for transmitting a first signal and a second signal. A variable reflector reflects a portion of the first signal at a first reflecting property to produce a first reflected signal, the portion of the first signal having traveled through the material. The variable reflector also reflects a portion of the second signal at a second reflecting property to produce a second reflected signal, the portion of the second signal having traveled through the material. A receiver receives the first received signal and the second received signal, the first received signal includes the first reflected signal having traveled through the material and the second received signal includes the second reflected signal having traveled through the material. The first reflected signal and the second reflected signal providing an indication of at least one property of the material. The at least one property includes permittivity, attenuation, anisotropy, and frequency dependency of the material.

RELATED PATENT APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/840,709, filed Jun. 28, 2013, and also claims the benefit of U.S.Provisional Application No. 61/840,742, filed Jun. 28, 2013, thedisclosures of which are both incorporated by reference herein in theirentirety.

FIELD

The present disclosure relates generally to the field of measurement ofat least one property of a material using reflectometry. Morespecifically, the embodiments of the present disclosure relate tomeasurement of at least one physical property of a material using avariable reflector that can be external to the material or embedded inthe material.

INTRODUCTION

Numerous methods have been used in the study of geologic materials tomeasure material properties of representative bulk samples. One topicarea of interest is the study of geologic materials to indirectlydetermine water content, such as described by Topp, G. C., J. L. Davis,and A. P. Annan, 1980: Electromagnetic determination of soil watercontent: Measurements in coaxial transmission lines. Water Resour. Res.16:574-582. A time-domain reflectometry method is used to measure watercontent in soils via sensing electrical properties (dielectricpermittivity) from the electromagnetic wave velocity at radio-wavefrequencies.

Many publications address the use of ultra-wide band ground penetratingradar to exploit various reflector characteristics to extracttravel-time and transmission amplitude variations in a material.Physical and empirical relationships are then used to estimate bulkdielectric constant (permittivity) and attenuation. Relationships, suchas disclosed in Topp et al, are used to further indicate relatedphysical properties such as water content, density, porosity and others.

An electromagnetic field impinging on conductive wire creates a currentflowing through the conductive wire, which then creates a secondaryelectromagnetic field in the space surrounding the wire. This is oftenknown as scattering. Wire antennas or scatters apply this phenomenon.For example, Kraus [1] provides a description of this phenomenon.

The response of a wire to an incident electromagnetic field can becomplex and is dependent on the electrical properties of the wire, thegeometrical shape of the wire, and properties of the environmentsurrounding the wire.

Examples of application of this phenomenon include repeaters, whichreceive an electromagnetic radio wave signal and then retransmit,amplify or somehow modify and resend the signal, a variety of targetdetection encoding and detecting methods such as RFID, and methods ofcalibrating radar systems and scatterometers. Examples of these can befound in references [2]-[7].

SUMMARY

The present disclosure provides in a first aspect a system for measuringa material. The system includes at least one transmitter fortransmitting at least a first signal and a second signal; at least onevariable reflector for reflecting a portion of the first signal at afirst reflecting property to produce a first reflected signal, theportion of the first signal having traveled through the material, andfor reflecting a portion of the second signal at a second reflectingproperty to produce a second reflected signal, the portion of the secondsignal having traveled through the material; at least one receiver forreceiving at least a first received signal and at least a secondreceived signal, the first received signal comprising the firstreflected signal having traveled through the material and the secondreceived signal comprising the second reflected signal having traveledthrough the material, the first reflected signal and the secondreflected signal providing an indication of at least one property of thematerial.

The present disclosure presents in another aspect a method for measuringa material. The method includes the steps of transmitting at least afirst signal into the material and a second signal into the material;controlling at least one reflector to reflect a portion of the firstsignal at a first reflecting property to produce a first reflectedsignal, the portion of the first signal having traveled through thematerial; controlling the at least one reflector to reflect a portion ofthe second signal at a second reflecting property to produce a secondreflected signal, the portion of the second signal having traveledthrough the material; receiving at least a first received signal and atleast a second received signal, the first received signal comprising thefirst reflected signal having traveled through the material and thesecond received signal comprising the second reflected signal havingtraveled through the material, the first reflected signal and the secondreflected signal providing an indication of at least one property of thematerial.

The present disclosure presents in yet another aspect a kit formeasuring a material. The kit includes at least one transmitter fortransmitting at least a first signal and a second signal, at least onevariable reflector for reflecting a signal at a first reflectingproperty and reflecting a signal at a second reflecting property, areceiver for receiving at least a first received signal and at least asecond received signal, and a non-transitory computer-readable mediumupon which a plurality of instructions are stored. The instructions arefor controlling at least one transmitter to transmit the first signal,controlling at least one transmitter to transmit the second signal,controlling at least one variable reflector to adjust the reflectingproperty of the reflected between the first reflecting property and thesecond reflecting property, and isolating a first reflected signal ofthe first received signal and a second reflected signal of the secondreceived signal.

The present disclosure provides in yet another aspect a variablereflector having a plurality of elongated conductive elementsinterconnected by at least one variable electrical impedance junctionelement, a variation of the impedance of the junction element varying ascattering electromagnetic field scattering from the plurality ofinterconnected elongated conductive elements when energized.

The present disclosure provides in yet another aspect a variablereflector having a plurality of elongated conductive elements forscattering electromagnetic field therefrom when energized; and a motorfor rotating the plurality of elongated conductive elements.

The present disclosure provides in yet another aspect a variablereflector having a plurality of elongated conductive elementsinterconnected by at least one variable electrical impedance junctionelement, a variation of the impedance of the junction element varying ascattering electromagnetic field scattering from the plurality ofinterconnected elongated conductive elements when energized. A first setof the plurality of elongated conductive elements is interconnected by afirst set of the at least one junction element and is supported on afirst electromagnetically permeable support layer and has a firstorientation and a second set of the plurality of elongated conductiveelements is interconnected by a second set of the at least one junctionelement and is supported on a second support layer and has a secondorientation that is different from the first orientation.

DRAWINGS

A detailed description of various exemplary embodiments is providedherein below with reference to the following drawings, by way of exampleonly, and in which:

FIG. 1 is a schematic diagram of a system for measuring a property of amaterial according to various exemplary embodiments;

FIG. 2 is a plan view of the measurement system in operation accordingto one exemplary embodiment;

FIG. 3 is a plan view of the measurement system in operation accordingto another exemplary embodiment;

FIG. 4 is a plan view of the measurement system in operation accordingto yet another exemplary embodiment;

FIG. 5 is a plan view of the measurement system in operation accordingto yet another exemplary embodiment;

FIG. 6 is a schematic diagram of an exemplary method for measuring aproperty of a sample material;

FIG. 7A is a schematic diagram of an exemplary method for determining atleast one property of a sample material;

FIG. 7B illustrates an exemplary signal of a first received signal;

FIG. 7C illustrates an exemplary signal of a second received signal;

FIG. 7D illustrates a differential signal;

FIG. 8 is a schematic diagram of an exemplary method for determining aproperty of a sample material

FIG. 9 is a schematic diagram of an exemplary unsynchronized method fordetermining a property of a sample material.

FIG. 10 is a perspective view of a kit for determining a property of asample material.

FIG. 11 is a perspective view of a kit for determining a property of asample material.

FIG. 12 illustrates a perspective view of one conductive elementaccording to various exemplary embodiments;

FIG. 13 illustrates a plan view of an exemplary interconnection ofconductive elements;

FIG. 14 illustrates a circuit diagram of the exemplary interconnectionof FIG. 12;

FIG. 15 illustrates a plan view of exemplary combination conductiveelements formed from the interconnection of conductive elements of FIG.12;

FIG. 16 illustrates a plan view of exemplary combination conductiveelements formed from the interconnection of conductive elements of FIG.12;

FIG. 17 illustrates a circuit diagram of the exemplary interconnectionof FIG. 12;

FIG. 18 illustrates a plan view of exemplary combination conductiveelements from the interconnection conductive elements of FIG. 17;

FIG. 19 illustrates a plan view of two variable reflectors according tovarious exemplary embodiments;

FIG. 20 illustrates a perspective view of a multi-directional variablereflector according to various exemplary embodiments;

FIG. 21 illustrates a perspective view of a multi-directional variablereflector according to various exemplary embodiments;

FIG. 22 illustrates a schematic diagram of an exemplary method fordesigning a variable reflector.

DESCRIPTION OF VARIOUS EMBODIMENTS

It will be appreciated that numerous specific details are set forth inorder to provide a thorough understanding of the exemplary embodimentsdescribed herein. However, it will be understood by those of ordinaryskill in the art that the embodiments described herein may be practicedwithout these specific details. In other instances, well-known methods,procedures and components have not been described in detail so as not toobscure the embodiments described herein. Furthermore, this descriptionis not to be considered as limiting the scope of the embodimentsdescribed herein in any ways, but rather as merely describing theimplementation of the various embodiments described herein.

Various known methods of using reflectometry measure properties of amaterial based on the reflection of signals from the surface of thematerial itself. By contrast, various systems, apparatus, methods andkits described herein do not depend on the direct reflective propertiesof the material, but instead use signal transmission through thematerial with reflection from at least one variable or modulatedreflector to determine at least one property of the material.

“Sample material” herein refers to a physical material under test andfor which at least one property of the material is not known and is tobe determined according to systems, apparatus, methods and kitsdescribed herein. At least one property of the sample material includes,but is not limited to, signal velocity, attenuation, directivity,dielectric permittivity, water content, degree of water hydration.

Referring to FIG. 1, therein illustrated is a schematic diagramaccording to various embodiments of a measurement system 100 formeasuring at least one property of a sample material. The measurementsystem 100 includes a transmitter 102, receiver 104, at least onevariable reflector 106.

The measurement system 100 can further include a controller 108.Alternatively, an external controller 108 can be connected to themeasurement system 100 to communicate with various components of themeasurement system 100.

The measurement system 100 can further include a signal processor forprocessing signals received by the receiver 104. In some cases, thesignal processor may be embedded with the controller 108. Alternatively,received signals can be sent to an external signal processor foranalysis.

Either one, or both, of the controller 108 and the signal processor maybe implemented in hardware or software, or a combination of both. It maybe implemented on a programmable processing device, such as amicroprocessor or microcontroller, Central Processing Unit (CPU),Digital Signal Processor (DSP), Field Programmable Gate Array (FPGA),general purpose processor, and the like. In some embodiments, theprogrammable processing device can be coupled to program memory, whichstores instructions used to program the programmable processing deviceto execute the controller. The program memory can include non-transitorystorage media, both volatile and non-volatile, including but not limitedto, random access memory (RAM), dynamic random access memory (DRAM),static random access memory (SRAM), read-only memory (ROM), programmableread-only memory (PROM), erasable programmable read-only memory (EPROM),electrically erasable programmable read-only memory (EEPROM), flashmemory, magnetic media, and optical media.

The transmitter 102 includes at least one transmitting element 110 andsignal generator unit 112. The signal generator unit 112 can create atleast one signal that can be then transmitted from the transmittingelement 110. For example, transmitting of a signal is controlled bycontrol signals received from the controller 108. For example, the typeof signal (ex: frequency, amplitude) and the timing of the signal to betransmitted can be controlled by the controller 108. For example, thesignal generator unit 112 can include a digital-to-analog convertor forconverting a digital signal received from the controller 108 into ananalog signal to be transmitted by the transmitting element 110.

The transmitting element 110 can have a defined directivity to minimizespurious signals. For example, the transmitting element 110 can have adirectivity such that a significant portion of the transmitted signaltravels through the sample material and is reflected by the variablereflector 106.

For example, the transmitting element 110 can be an antenna capable ofemitting radio frequency signals generated by the signal generator unit112. However, it will be understood that other types of suitabletransmitting elements 110 can be used for transmitting other types ofsignals generated by the signal generator unit 112. For example,transmitting element 110 can be a speaker for emitting acoustic signalsgenerated by the signal generator unit 112. Alternatively, thetransmitting element 110 can emit various types of elastic waves. Thetransmitting element 110 can be other suitable transducer element foremitting signal waves.

The receiver 104 includes at least one receiving element 114 forreceiving signals and signal receiver unit 116. For example, the signalreceiver unit 116 includes an analog-to-digital converter for convertinga received analog signal to a digital signal. For example, the signalreceiver unit 116 is in communication with the controller 108 or signalprocessor and can send received signals to the controller 108 or signalprocessor for analysis. Alternatively, received signals can be partiallyor completely analyzed by the signal receiver unit 116. The type of thereceiving element 114 can be chosen based on the type of signals emittedfrom the transmitting element 110. For example, the receiving element114 can be a receiving antenna for receiving radio frequency waves, or amicrophone for receiving acoustic signals, or another type of elementfor receiving other types of waves.

The variable reflector 106 can reflect signals sent from thetransmitting element 110. The variable reflector 106 can becharacterized according to at least one reflecting property. “Reflectingproperty”, as used herein refers to a property of the variable reflector106 that can be characterized by the manner in which the variablereflector 106 changes an incident signal when reflecting that signal.For example, depending on the nature of the signal, one or morereflecting properties can be selected for the variable reflector 106.For example, where the signal sent from the transmitting element 110 ischaracterized by a vector wavefield, the reflecting property can bereflectivity amplitude of the variable reflector 106, which can beindependent of the incident excitation vector direction of the vectorwavefield. Alternatively, the reflecting property can be thereflectivity amplitude of the variable reflector 106 that is dependenton the incident excitation vector direction (often referred to as fieldpolarization) or anisotropy. For example, the reflectivity of thevariable reflector 106 can also depend on excitation frequency. In someembodiments, the selected reflectivity of the variable reflector 106 candepend on a combination of the above.

For example, as shown in FIG. 1, the variable reflector 106 is connectedto the controller 108 via one or more control lines and the selection ofthe reflecting property of the variable reflector 106 can be controlledby the controller 108. Accordingly, the timing of the selection of thereflecting property of the variable reflector 106 can be synchronizedwith the timing of the transmission of signals from the transmittingelement 110. Alternatively, the variable reflector 106 is not incommunication with the controller 108, and the adjusting of thereflecting property of the variable reflector 106 is made independentlyof the timing of the transmissions of the signal from the transmittingelement 110.

According to various exemplary embodiments, the transmitting element 110is mountable near or onto a surface of the sample material such thatalong at least one path, signals transmitted by the transmitting element110 substantially only travel through the sample material. In otherexemplary embodiments, transmitting element 110 can be positioned withinthe sample material, such as embedded within the sample material.

According to various exemplary embodiments, the receiving element 114 ismountable near or onto a surface of the sample material such that alongat least one path, signals received by the receiving element 114 willsubstantially only have traveled through the sample material. In otherembodiments, the receiving element 114 can be positioned within thesample material, such as embedded within the sample material.

According to various exemplary embodiments, the transmitter 102 and thereceiver 104 are in one-way or mutual communication. For example, thetransmitter 102 can communicate to the receiver 104 the time at whichthe transmitter 102 transmits a signal. Alternatively, the transmitter102 and the receiver 104 are controlled by the controller 108. Forexample, the controller 108 can control when the transmitter 102transmits a signal and when the receiver 104 begins receiving signals.In other exemplary embodiments, both the transmitter 102 and thereceiver 104 have internal clocks, and synchronization between thereceiver 104 and the transmitter 102 can be achieved through use of theinternal clocks.

According to various exemplary embodiments, the variable reflector 106is decoupled from the transmitter 102 and the receiver 104. The variablereflector 106 can be out of communication with the transmitter 102, thereceiver 104 and the controller 108. For example, each of thetransmitter 102 and the controller 108 can have internal clocks andsynchronization between the transmitter 102 and the controller 108 canbe achieved through use of the internal clocks. For example, the time oftransmitting a signal from the transmitter 102 and the time foradjusting the reflecting property of the variable reflector 106 can besynchronized. Alternatively, the transmitter 102 and the variablereflector 106 are not in synchronization and the adjustment of thereflecting property of the variable reflector 106 is carried outindependently of the timing of the transmission of a signal from thetransmitter 102.

According to various exemplary embodiments, the variable reflector 106is mountable near or onto a surface of the sample material such thatalong at least one path, signals reflected by the variable reflector 106will substantially only travel though the sample material.

According to various exemplary embodiments, the measurement system 100further includes a mount. For example, the mount is a container forholding the sample material. Alternatively, the mount can be used tomount components of the measurement system 100 onto the surface of asample material. The mount can be formed of a material that istransparent at a range of frequencies corresponding to the range atwhich signals are transmitted from the transmitting element 110. Forexample, the transmitting element 110 can be attached to the mount suchthat during measurement operation, the transmitting element 110 ispositioned near or onto to the surface of the sample material and thatalong at least one path, signals transmitted by the transmitting element110 substantially only travels through the sample material. For example,the receiving element 112 can be attached to the mount such that duringmeasurement operation, the receiving element 114 is positioned near oronto the surface of the sample material and that along at least onepath, signals received by the receiving element 116 will substantiallyonly have traveled through the sample material. For example, thevariable reflector 106 can be attached to the mount such that duringmeasurement operation, the variable reflector 106 is positioned close tothe surface of the sample material and that along at least one path,signals reflected by the variable reflector 106 will substantially onlytravel though the sample material.

Referring now to FIG. 2, therein illustrated is a plan view of themeasurement system 100 in operation for measuring at least one propertyof a sample material 118 according to one exemplary embodiment. Atransmitting element 110 of the transmitter 102 is mounted near or ontoa surface of the sample material 118. A receiving element 114 of thereceiver 104 is also mounted near or onto the surface of the samplematerial 118 and is spaced apart from the transmitting element 110. Atransmitted signal 120 is transmitted from the transmitter 102. Thetransmitted signal 120 can be modeled as traveling over two signal pathsbetween the transmitting element 110 and the receiving element 114. Aportion of the transmitted signal 120 travels over a reflected signalpath 122 defined by vectors A and A′. Over the reflected signal path122, the portion of the transmitted signal 120 propagates through thesample 118 material along the vector A to reach a reflecting surface 124of the variable reflector 106. The portion of the transmitted signal 120is reflected by the variable reflector 106 and a reflected signal 126 isproduced. The reflected signal 126 then propagates through the samplematerial 118 along the vector A′ to reach the receiving element 114 ofthe receiver 104.

Another portion of the transmitted signal 120 travels over anunreflected signal path 123 defined by vector B. Over the unreflectedsignal path 123, the portion of the transmitted signal 120 is notreflected by the variable reflector 106. This portion of the transmittedsignal 120 is represented as an unreflected signal 128. The unreflectedsignal 128 propagates through the sample material 118 or outside of thesample material 118 along the unreflected signal parth 123 to reach thereceiving element 114 of the receiver 102.

It will be appreciated that a received signal 130 received at thereceiving element 114 by the receiver 104 includes the unreflectedsignal 128, corresponding to a portion of the transmitted signal 120that is not reflected by variable reflector 106, and includes thereflected signal 126, corresponding to a portion of the transmittedsignal 120 that is reflected by the variable reflector 106.

It will be understood that the reflected signal path 122 defined byvectors A and A′ and the unreflected signal path 123 defined by vector Bare illustrated as an exemplary model. In operation, there may be aplurality of additional paths between the transmitter 102 and thereceiver 104. However, each of these additional paths can also bemodeled in the same manner as the reflected signal path 122 orunreflected signal path 123.

Referring now to FIG. 3, therein illustrated is a plan view of themeasurement system 100 in operation for measuring at least one propertyof the sample material 118 according to one exemplary embodiment. Asshown, the sample material 118 has a substantially circular crosssection. For example, the sample material 118 can be a pipe, a pole,mining core, or a natural object such as a tree trunk. However, it willbe understood that a sample material 118 having other shapes may beused. The transmitting element 110 is mounted to a surface of the samplematerial 118. Preferably, the transmitting element 110 forms a tangentwith the surface of the sample material 118. The receiving element 114is mounted near or onto a surface of the sample material 118.Preferably, the receiving element 114 also forms a tangent with thesurface of the sample material 118. The variable reflector 106 ismounted such that the reflecting surface 124 of the variable reflectorcontacts the sample material 118. Preferably, the reflecting surface 124also forms a tangent with the surface of the sample material 118.

Referring now to FIG. 4, therein illustrated is a plan view of themeasurement system 102 in operation for measuring at least one propertyof the sample material 118 according to one exemplary embodiment. Thesample material 118 can be a wall or a slab having a large width and/orlength. The transmitting element 110 and receiving element 114 aremounted onto a first surface of the sample material 118. The variablereflector 106 is mounted near or onto a second surface that is oppositethe first surface. For example, the variable reflector 106 can bedecoupled from the transmitter 102, receiver 104 and/or controller 108.This may be due to the significant size of the sample material 118,which makes it impractical to maintain coupling of the variablereflector 106 with the transmitter 102 and receiver 104 side of themeasurement system 100. The variable reflector 106 can also be out ofcommunication with the transmitter 102 and receiver 104 side of thevariable reflector 106.

Referring now to FIG. 5, therein illustrated is a plan view of themeasurement system 100 in operation for measuring at least one propertyof the sample material 118 according to one exemplary embodiment. Thetransmitting element 110 and receiving element 114 are mounted near oronto a surface of the sample material 118. The variable reflector 106 isplaced inside the sample material 118. For example, the variablereflector can be embedded inside the sample material 118. For example,the sample material 118 can be a fluid material, and the variablereflector 116 can be inserted into the sample material 118.

Referring now to FIG. 6, therein illustrated is a schematic diagram ofan exemplary method 900 for measuring a property of a sample material.For example, the method 900 can be carried out using the measurementsystem 100 described herein.

At step 904 a first signal 120 is transmitted into the sample material118. For example, the first signal 120 can be transmitted from thetransmitting element 110. For example, the first signal 120 can be atransient signal. For example, the transient signal can be a Gaussian,an error function wavelet or a Ricker wavelet. Alternatively, the firstsignal 120 can be a periodic signal.

A portion of the first signal 120 transmitted into the sample material118 travels through the sample material 118 and is reflected by areflector at step 908 at a first reflecting property. For example, thefirst signal 120 is reflected by variable reflector 106 that has beenadjusted to have the first reflecting property. A first reflected signal126 is produced from the portion of the first signal 120 beingreflected. The first reflected signal 126 continues to propagate throughthe sample material 118.

At step 912, a first received signal 130 is received. For example, thefirst received signal 130 is received by the receiving element 114 ofreceiver 104. The first received signal 130 includes the first reflectedsignal 126 that traveled through the sample material 118 and also anunreflected portion 128 of the first transmitted signal 120.

Referring back to FIGS. 2-5, a portion of the first signal 120transmitted into the sample material 118 can be generally modeled ashaving traveled over the path defined by vector A to reach the reflector106. After being reflected by the reflector 106, the first reflectedsignal 126 that is produced can be generally modeled as having traveledover the path denoted by the vector A′ to reach the receiver 104. Thefirst reflected signal 126 represents the portion of the firsttransmitted signal 120 that traveled over the path AA′.

Continuing with FIGS. 2-5, the unreflected portion 128 of the firsttransmitted signal 128 can be generally modeled as having traveled overthe path denoted by the vector B to reach the receiver 104 without beingreflected by the variable reflector 106.

At step 920 a second signal 120 is transmitted into the sample material118. For example, the second signal 120 is also transmitted from thetransmitting element 110. For example, the first signal 120 and thesecond signal 120 have substantially the same characteristics. Forexample, the first signal 120 and the second signal 120 can beidentical. According to various exemplary embodiments, the transmittingof the first signal 120 and the transmitting of the second signal 120can be spaced apart temporally. For example, the transmitting of thefirst signal 120 and the transmitting of the second signal 120 can bespaced apart for a duration of time that is greater than the timerequired to adjust the reflecting property of the variable reflector 106from a first reflecting property to a second reflecting property. Forexample, the transmitting of the first signal 120 and the transmittingof the second signal 120 can be spaced apart for a duration of time thatis greater than the time required for a first signal 120 to be reflectedby a reflector and for the first received signal 130 to be received atthe receiving element 114.

A portion of the second signal 120 transmitted into the sample material118 travels through the material and is reflected by a reflector at step924 at a second reflecting property. According to various exemplaryembodiments, the value of the second reflecting property is differentfrom the value of the first reflecting property. For example, the secondsignal 120 is reflected by variable reflector 106 that has been adjustedto have the second reflecting property. A second reflected signal 126 isproduced from the portion of the second signal 120 being reflected. Thesecond reflected signal 126 continues to propagate through the samplematerial 118.

Between the time the portion of the first signal 120 is reflected andthe portion of the second signal 120 is reflected, the reflectingproperty of the reflector is modified from the first reflecting propertyto the second reflecting property. For example, the reflecting propertycan be modified by manually replacing a first reflector having the firstreflector property with a second reflector having a second reflectorproperty. According to exemplary embodiments where the variablereflector 106 is used to reflect the first signal 120 and second signal120, the variable reflector 106 is controlled, for example by controller108, to be adjusted from the first reflecting property to the secondreflecting property prior to reflecting the portion of the second signal120.

According to various exemplary embodiments where the transmitting ofsignals from the transmitter 102 is synchronized with the adjusting ofthe reflecting property of the variable reflector 106, the variablereflector 106 is controlled to be adjusted to the first reflectingproperty before the transmitter 102 transmits the first signal 120.After reflecting the portion of the first signal 120, the variablereflector is controlled to be adjusted to the second reflectingproperty. After the variable reflector 106 is adjusted to the secondreflecting property, the transmitter 102 transmits the second signal 120at step 920. For example, synchronization of the transmitter 102 withthe variable reflector 106 is maintained through control provided by thecontroller 108.

At step 928, a second received signal is received. For example, thesecond received signal is received by the receiving element 114 ofreceiver 104. The second received signal includes the second reflectedsignal 126 that traveled through the sample material 118 and also anunreflected portion 128 of the second transmitted signal 120.

Referring back to FIGS. 2-5, a portion of the second signal 120transmitted into the sample material 118 can be generally modeled asalso having traveled over the path defined by vector A to reach thereflector 106. After being reflected by the reflector 106, the secondreflected signal 126 that is produced can be generally modeled as alsohaving traveled over the path denoted by the vector A′ to reach thereceiver 104. The second reflected signal 126 represents a portion ofthe second transmitted signal 120 that also traveled over the path 122defined by vectors A and A′. The unreflected portion 128 of the secondtransmitted signal 120 can be generally modeled as also having traveledover the path denoted by the vector B to reach the receiver 104 withoutbeing reflected by the reflector 106. The first reflected signal 128 andthe second reflected signal 128 provide an indication of at least oneproperty of the sample material 118. By temporally spacing the firstsignal 120 and the second signal 120 apart from one another, the firstreflected signal 128 and the second reflected signal 128 can be observedindependently of one another.

Determining a Scalar-Type Property of the Material

Referring now to FIG. 7A, therein illustrated is a schematic diagram ofan exemplary method 1000 for determining at least one property of thesample material 118 based on the first received signal and the secondreceived signal.

The first received signal can be expressed as:

o _(i)(t)=b _(i)(t)+a _(i)(t)+n _(i)(t)

where b_(i)(t) is the unreflected portion 128 of the first transmittedsignal 120, a_(i)(t) is the first reflected signal 126, and n_(i)(t) israndom noise. For example, where the first received signal is renderedin discrete sampling data point format, o_(i)(t) can be referred to as atrace or a time series of observation points.

Similarly, the second received signal can be expressed as:

o _(k)(t)=b _(k)(t)+a _(k)(t)+n _(k)(t)

where b_(k)(t) is the unreflected portion 128 of the second transmittedsignal 120, a_(k)(t) is the second reflected signal 126, and n_(k)(t) israndom noise. For example, where the first received signal is renderedin discrete sampling data point format, o_(k) (t) can be referred to atrace or a time series of observation points.

Referring back to FIG. 2, the signal path 122 traveled by the reflectedsignal 126 and generally defined by vectors A and A′ can be modeled ashaving a path length L_(a). Accordingly, there is a time delay T_(a)between the time the transmitted signal 120 is transmitted from thetransmitter 102 and the time the reflected signal 126 is received at thereceiver 104. Since the first reflected signal 126 and the secondreflected signal 126 both represent portions of transmitted signals thatpropagated over the signal path 122 defined by vectors A and A′, andthat both signals have the same velocity v_(a) when traveling throughthe sample material 118, the time delay between the transmitting of asignal from the transmitter 102 and the receiving of the reflectedsignal 126 can be represented as:

$T_{a} = \frac{L_{a}}{v_{a}}$

The unreflected signal 128 travels over a signal path defined by vectorB can be modeled as having a path length L_(b). Accordingly, there is atime delay T_(b) between the time the transmitted signal 120 istransmitted from the transmitter 102 and the time the unreflected signal128 is received at the receiver 104. Since the unreflected first signal128 and unreflected second signal 128 both represent portions of thetransmitted signals that propagated over the signal path 123 defined byvector B, and have the same velocity v_(b), the time delay between thetransmitting of a signal from the transmitter 102 and the receiving ofthe unreflected signal 128 can be represented as:

$T_{b} = \frac{L_{b}}{v_{b}}$

According to various exemplary embodiments where the first transmittedsignal 120 and the second transmitted signal 120 have substantially thesame characteristics and is a transient signal, both signals can berepresented by a wavelet w(t). Assuming that the wavelet signal w(t) isnot substantially distorted over either reflected signal path 122 orunreflected signal path 123, an observation of the first received signalcan be represented as:

o _(i)(t)=b w(t−T _(b))+M _(i) w(t−+n _(i)(t)

where b represents the amplitude of signal coupling over the unreflectedpath 123, b w(t−T_(b)) represents the unreflected first signal 128,M_(i) represents the value of the amplitude of signal coupling over thereflected signal path 122 combined with the first reflecting property atwhich the portion of the first transmitted signal 120 is reflected, andM_(i) w(t−T_(a)) represents the first reflected signal 126.

It will be understood that term of “amplitude of signal coupling” asused herein represents the factor of a change in the amplitude of aportion of a received signal (for example a portion representing theunreflected signal or a second portion representing the reflectedsignal) in relation to the transmitted signal. For example, theamplitude of signal coupling can depend on the properties of the system,such as properties of a container used to hold the sample material. Theamplitude of signal coupling can also depend on properties of thematerial, including material absorption or attenuation.

An observation of the second received signal can be represented as:

o _(k)(t)=b w(t−T _(b))+M _(k) w(t−+n _(k)(t)

where b represents the attenuation over the unreflected path B, bw(t−T_(h)) represents the unreflected second signal 128, M_(j)represents the value of the amplitude of signal coupling over thereflected signal path combined with the second reflecting property atwhich the portion of the second transmitted signal 120 is reflected, andM_(k) w(t−T_(a)) represents the second reflected signal 126.

Observation o_(i)(t) corresponds to an observation made by the receiver104 between the time first reflected signal 120 is transmitted and thetime the receiving of the first reflected signal 126 is completed.Observation o_(k)(t) corresponds to an observation made by the receiver104 between the time second reflected signal 120 is transmitted and thetime the receiving of the second reflected signal 126 is completed. Forexample, the transmitter 102 and the receiver 104 can be synchronizedsuch that a receiver 104 begins an observation when transmitter 102transmits a signal into the sample material 106. It will be appreciatedthat while the transmission of the first signal 120 and the transmissionof the second signal 120 can be spaced apart temporally, M_(i)w(t−T_(a)) and M_(k) w(t−T_(a)) representing the first reflected signal126 and second reflected signal 126 respectively both have the same timedelay T_(a) in observations o_(i)(t) and o_(k)(t).

At step 1004, the first reflected signal 126 and the second reflectedsignal 126 are isolated. For example, the reflected signals can beisolated by calculating a difference between the observation o_(i)(t) ofthe first received signal 126 and the observation o_(k)(t) of the secondreceived signal 126. For example, the difference can be calculated bythe signal processor in the measurement system 100 or by the externalsignal processor. The result of the difference can be represented as:

o _(i)(t)−o _(k)(t)=(M _(i) −M _(k))w(t−T _(a))+n _(i)(t)−n _(k)(t)

It will be appreciated that because the first transmitted signal 120 andthe second transmitted signal 120 have substantially the samecharacteristics, and that the unreflected first signal 128 and thesecond unreflected signal 128 both represent signals having traveledover the same path B, the unreflected portions 128 of the first signal120 and the unreflected portion 128 of the second signal 120 arecancelled out from calculating a difference between the observationo_(i)(t) of the first received signal and the observation o_(k)(t) ofsecond received signal. By contrast, due to reflecting the first signal120 and the second signal 120 at different reflecting properties,calculating the difference between observation o_(i)(t) and o_(k)(t)leaves a non-zero portion (M_(i)−M_(k))w(t−T_(a)) representing the firstreflected signal 126 and second reflected signal 126. For example, wherethe first reflecting property is a first reflectivity and the secondreflecting property is a second reflectivity different from the firstreflectivity, the resulting non-zero portion is similar to thetransmitted first signal 120 or second signal 120, but having adifferent amplitude. Accordingly, the first reflected signal 126 and thesecond reflected signal 126 are isolated.

According to various exemplary, where the amplitude of the isolatedfirst reflected signal and second reflected signal 126 is sufficientlyhigh, the noise portions n_(i)(t)−n_(k)(t) of the first received signaland the second received signal can be negligible with respect to thefirst reflected signal 126 and second reflected signal 126. Accordingly,the noise portions can be omitted.

Alternatively, where the noise is random and zero mean in character,steps 904 to 928 of method 900 can be repeated a plurality of times,each time using a consistent first reflecting property at step 912 and aconsistent second reflecting property at step 924. Furthermore, thedifference between the first received signal and the second receivedsignal can be calculated for each repetition of steps 904-928. Theplurality of the calculated differences can be averaged to furtherisolate the first reflected signal 126 and the second reflected signal126. For example, the noise portion of the averaged calculateddifference can be represented as:

n _(j)(t)−n _(k)(t)

=0

where the <a> expression denotes an expected or average value (ex:

$< a>=\frac{\sum\limits_{i}\; a_{i}}{N}$

where i=1 to N)

For example, the isolated first and second reflected signals can berepresented as:

o _(j)(t)−o _(k)(t)

=(M _(j) −M _(k))w(t−T _(a))

At step 1008, the time delay, of the isolated first and second reflectedsignals is determined. The delay can be determined according to an eventpicking or identification process that defines where a characteristic ofthe excitation signal occurs in time. This delay represents the timerequired by a transmitted signal 120 transmitted from the transmitter102 traveling over the reflected path 122 defined by vectors AA′ toreach the receiver 104 as a received signal 130. For example, this delayis represented by T_(a). Where the transmitted signal 120 is a compactpulse of a short oscillatory signal, or similar excitation waveform,determination or estimation of delay T_(a) can be carried out accordingto known methods commonly used in analysis of seismic data, ultrasonicdata or similar data.

At step 1012, a property of the material is determined based on thedelay. For example, the electrical permittivity of the material affectsthe velocity at which a signal travels through the material. Preferably,the first and second reflecting properties are different reflectivitywhen carrying out step 1012 to determine the electrical permittivity ofthe sample material. However, other types of reflecting properties canalso be used. Referring back to FIGS. 2 to 5, if the length of thereflected signal path 122 is known, the velocity v_(a) of a signal canbe calculated according to:

$v_{a} = \frac{L_{a}}{T_{a}}$

If the measurement apparatus measures electromagnetic wave properties,then it is common practice to estimate the dielectric permittivity, K,of the material using the relationship:

$K = {\left( \frac{c}{v_{a}} \right)^{2} = \left( \frac{{cT}_{a}}{L_{a}} \right)^{2}}$

where c is the speed of light in vacuum. For example, the calculationsof the velocity and permittivity can be carried out by the signalprocessor in the measurement system 100 or external to the measurementsystem 100.

According to an alternative exemplary embodiment, the first transmittedsignal 120 and second transmitted signals 120 are periodic signals. Thefirst transmitted signal 120 and second transmitted signal 120 havesubstantially the same characteristics. For example, the periodictransmitted signal can be represented by:

w(t)=e ^(jωt)

where j=√{square root over (−1)}.

Assuming that the w(t) is not substantially distorted over either pathAA′ or path B, the first received signal can be represented as:

o _(i)(t)=be ^(jωt) +M _(i) e ^(jωt) e ^(−jωT) ^(a) +n _(i)(t)

where b represents the attenuation over the unreflected path B, be^(jωt)represents the unreflected first signal 128, M_(i)e^(jωt)e^(−jωt) ^(a)represents the first reflected signal 126, and M_(j) represents thevalue of the first reflecting property at which the portion of the firsttransmitted signal 120 is reflected.

The second received signal can be represented as:

o _(k)(t)=be ^(jωt) +M _(k) e ^(jωt) e ^(−jωT) ^(b) +n _(k)(t)

where b represents amplitude of signal coupling over the reflectedsignal path path 123, be^(jωt) represents the unreflected second signal128, M_(i)e^(jωt)e^(−jωT) ^(a) represents the second reflected signal128, and M_(k) represents amplitude of signal coupling over thereflected signal path combined with the second reflecting property atwhich the portion of the second transmitted signal 120 is reflected.

At step 1004, the first reflected signal 126 and the second reflectedsignal 126 are isolated by also calculating a difference between thefirst and the second received signals. For example, the difference canbe calculated by the signal processor in the measurement system 100 orthe signal processor external to the measurement system 100. The resultof the difference can be represented as:

O _(i) −O _(k) =e ^(−iωT) ^(a) (M _(i) −M _(k))+n _(i)(t)−n _(k)(t)

It will be appreciated that because the first transmitted signal 120 andthe second transmitted signal 120 have substantially the samecharacteristics, and that the unreflected first signal 128 and thesecond unreflected signal 128 both represent signals having traveledover the same unreflected signal path 123, the unreflected portion 128of the first signal 120 and the unreflected portion 128 of the secondsignal 120 are canceled out from calculating a difference between theobservation o_(i)(t) of the first received signal and the observationo_(k)(t) of second received signal. By contrast, reflecting the firstsignal 120 and the second signal 120 at different reflecting properties,calculating the difference between observation o_(i) (t) and o_(k)(t)leaves a non-zero portion representing the first reflected signal 126and second reflected signal 126. For example, where the first reflectingproperty is a first reflectivity and the second reflecting property is asecond reflectivity different from the first reflectivity, the resultingdifference is similar to the transmitted first signal 120 or secondsignal 120, but having a different amplitude. Accordingly, the firstreflected signal 126 and the second reflected signal 126 are isolated.

According to various exemplary, where the amplitude of the isolatedfirst reflected signal 126 and the second reflected signal 126 issufficiently high, the noise portions n_(i)(t)−n_(k)(t) of the firstreceived signal and the second received signal can be negligible withrespect to the first reflected signal 126 and second reflected signal126. Accordingly, the noise portions can be omitted.

Alternatively, where the noise is random and zero mean in character,steps 904 to 928 of method 900 can be repeated a plurality of times,each time using a consistent first reflecting property at step 912 and aconsistent second reflecting property at step 924. Furthermore, thedifference between the first received signal and the second receivedsignal can be calculated for each repetition of steps 904-928. Theplurality of calculated differences can be averaged to further isolatethe first reflected signal and the second reflected signal. For example,the noise portion of the averaged calculated difference can berepresented as:

n _(j)(t)−n _(k)(t)

=0

where the <a> expression denotes an expected or average value.

For example, the isolated first reflected signal 126 and secondreflected signal 126 can be represented as:

O _(i) −O _(k)

=e ^(−iωT) ^(a) (M _(i) −M _(k))

At step 1008, a phase delay of the isolated first and second reflectedsignals is determined. This phase delay represents the time required bytransmitted signal 120 transmitted from the transmitter 102 travelingover the path AA′ to reach the receiver 104 as a reflected signal 126.For example, this delay is represented by φ_(a)=ωT_(a). The phase delaycan be determined using techniques known in the art, such as waveformdigitization, Fourier transform, phase locked measurements, signalmixing.

At step 1012, a property of the material is determined based on thedelay. For example, the electrical permittivity of the material affectsthe velocity at which a signal travels through the material. Preferably,the first and second reflecting properties are different reflectivitieswhen carrying out step 1012 to determine the electrical permittivity ofthe sample material. However, other types of reflecting properties canalso be used. Referring back to FIGS. 5 to 8, if the length of thesignal path 122 is known, the velocity of a signal can be calculatedaccording to:

$v_{a} = {\frac{L_{a}}{T_{a}} = \frac{L_{a}\omega}{\phi_{a}}}$

If the measurement apparatus measures electromagnetic wave properties,then it is common practice to estimate the dielectric permittivity, K,of the material using the relationship:

$K = {\left( \frac{c}{v_{a}} \right)^{2} = \left( \frac{{cT}_{a}}{L_{a}} \right)^{2}}$

where c is the speed of light in vacuum. For example, the calculationsof the velocity and permittivity can be carried out by the signalprocessor the measurement system 100.

Referring now to FIGS. 7B to 7D, therein illustrated are exemplarysignals of a first received signal 1016, a second received signal 1020and a differential signal 1024 representing a difference between thefirst and second received signals, respectively. The first receivedsignal 1016 and second received signal 1020 are illustrated to bealigned in time according to a signal start time 1028. A time delay 1032represents the time required by transmitted signal 120 transmitted fromthe transmitter 102 traveling over the path AA′ to reach the receiver104 as a reflected signal 126 (as either first received signal 1016 orsecond received signal 1020). Between the signal start time 1028 andtime delay 1032 only the unreflected portion 128 is received. It will beappreciated that this unreflected portion 128 is the same in the firstreceived signal 1016 and the second 1020, such that taking a differenceof the two signals results in differential signal 1024 having asubstantially zero amplitude signal between its signal start time 1128and the time delay 1032. Moreover, due to the first transmitted signal120 and the second transmitted signal 120 being reflected at differentreflecting properties at the reflector 106, the first received signal1016 and the second received signal 1020 have different amplitudes.However, since both the first received signal 1016 and the secondreceived signal 1020 include a same unreflected portion 120, thisportion 120 is cancelled out in the differential signal 1024. Thedifferential signal 1024 at times after the travel time delay resemblethe transmitted signals 120, 120 (and also the unreflected portion 128before the time delay), but has a different amplitude due to the firstand second transmitted signals 120, 120 being reflected at differentreflecting properties.

Determining a Orientation-Dependent Property of the Material

According to one exemplary embodiment, method 900 may be carried out toallow determination of anisotropy of a property of the sample material118. Accordingly, steps of the method 900 are carried out a first time.During the first time, the first signal 120 is transmitted at step 904and is subsequently reflected at step 908 such that the first receivedsignal 130 is characterized by a first polarization of the signal. Thereceived signal is sensitive to the specific transmitted signalpolarization. Similarly, the second signal 120 is transmitted at step920 and is subsequently reflected at step 924 such that the secondreceived signal is also characterized by the first polarization of thesignal. The first received signal 130 and the second received signal 130provide an indication of the property of the sample material 118 for afirst direction corresponding to the first polarization.

The steps of method 900 are then carried out a second time. During thesecond time, a third signal 120 is transmitted at step 904 and issubsequently reflected at step 908 such that the third received signal130 is characterized by a second polarization of the signal that isdifferent from the first polarization. For example, the secondpolarization is orthogonal to the first polarization. The receivedsignal is sensitive to the specific transmitted signal polarization.Similarly, a fourth signal 120 is transmitted at step 920 and issubsequently reflected at step 924 such that the second received signal130 is also characterized by the second polarization, which can bedifferent and, in some cases, orthogonal to the first polarization. Thethird received signal and the fourth received signal then provide anindication of the property of the sample material 118 for a secondorientation corresponding to the second polarization. The degree towhich the property of the sample material 118 changes with differentpolarizations provides an indication of the anisotropy of a property ofthe sample material 118. Those skilled in the art will furtherunderstand that indications of anisotropy of a property of the samplematerial 118 in at least two directions can be used to determineanisotropy of the property over a range of direction. For example,indications of anisotropy of the property of the sample material 118 inthe first direction and the second orthogonal direction can be used tofully characterize the anisotropy of the material of the sample material118. Indications of anisotropy of the property of the sample material118 in different directions can be further used to determine that thesample material isotropic.

According to one exemplary embodiment, the transmitting element 110 isadjustable to emit signals at different polarizations. For example, thetransmitting element 110 can be a dual transmitting element capable ofselectively transmitting signals at the first polarization or the secondpolarization. In some cases, the first polarization and the secondpolarization are orthogonal to each other. Alternatively, transmittingelement 110 includes a rotatable element, wherein rotation of theelement provides adjustment of the polarization of the signals 120emitted from the transmitting element 110. For example, the element 110can be attached to a rotatable mount.

Similarly, the receiving element 114 is also adjustable to receivesignals at different polarizations. For example, the receiving element114 can be a dual receiving element capable of selectively receivingsignals at the first polarization or the second polarization. In somecases, the first polarization and the second polarization are orthogonalto each other. Alternatively, the receiving element 114 includes arotatable element, wherein rotation of the element provides adjustmentof polarization of the signals that can be received by the receivingelement 114. For example, the receiving element 114 can be attached to arotatable mount.

Where transmitting element 110 and receiving element 114 are adjustableand selectable in polarization, the variable reflector 106 is notrequired to have a field directional reflectivity dependence althoughthe reflector 106 must have an adjustable reflectivity to modulate theamplitude of the reflected signals.

Referring back to FIG. 6, when carrying out the method 900 according tovarious exemplary embodiments using adjustable transmitting element 110and adjustable receiving element 114 to determine anisotropy of aproperty of the sample material, at step 904, the first signal 120 istransmitted at the first polarization.

At step 908, the portion of the first signal 120 travelling through thesample material 118 is reflected at a first reflecting property. Forexample, the first signal 120 is reflected by the variable reflector 106that has been adjusted to a first reflectivity. Due to the reflecting,the amplitude of the first reflected signal 126 can be different fromthe first signal 120, while the polarization of the first reflectedsignal 126 is maintained in relation to the first signal 120.

At step 912, the first received signal is received. For example, thefirst received signal 1300 is received by the receiving element 114 ofreceiver 104. The first received signal includes the first reflectedsignal 126 that traveled through the sample material 118 with thedefined first polarization and also an unreflected portion 128 of thefirst transmitted signal 120.

At step 920, the second signal 120 is transmitted at the firstpolarization, which is the same polarization as the first signal 120.

At step 924, the portion of the second signal 120 travelling through thesample material 118 is reflected at a second reflecting property. Forexample, the second signal 120 is reflected by the variable reflector106 that has been adjusted to a second reflectivity different from thefirst reflectivity. For example, the variable reflector 106 is adjustedto the second reflectivity after reflecting the first signal 120 andprior to reflecting the second signal 120. Due to the reflecting, theamplitude of the second reflected signal 126 can be different from thesecond signal 120. The amplitude of the second reflected signal 126 isalso different from the amplitude of the first reflected signal 126,while the polarization of the second reflected signal 126 is the same asthe polarization of the first reflected signal 126.

At step 928, the second received signal is received. For example, thesecond received signal is received by the receiving element 114 ofreceiver 104. The second received signal includes the second reflectedsignal 126 that traveled through the sample material 118 with thedefined polarization and also an unreflected portion 128 of the secondtransmitted signal 120.

The first received signal 130 and the second received signal 130 can beused to determine a physical property for a first directioncorresponding to the first defined polarization of the exciting waveformsignals 120 and 120.

Continuing with FIG. 6, the method 900 can be carried out a second time,wherein a third signal and fourth signal are transmitted at steps 904and 920 respectively at a second polarization. The second polarizationis different from the first polarization at which the first and secondsignals were transmitted. For example, the second polarization isorthogonal to the first polarization. At step 904, a third signal 120 istransmitted at the second polarization.

At step 908 of the second time of carrying out method 900, the portionof the third signal 120 travelling through the sample material 118 isreflected at a first reflecting property. For example, the third signal120 is reflected by the variable reflector 106 that has been adjusted toa first reflectivity. Due to the reflecting, the amplitude of the thirdreflected signal 126 can be different from the third signal 120, whilethe polarization of the third reflected signal 126 is maintained inrelation to the third signal 120.

At step 912, the third received signal with the different fieldpolarization is received. For example, the third received signal isreceived by the receiving element 114 of receiver 104. The thirdreceived signal includes the third reflected signal 126 that traveledthrough the sample material 118 with the defined polarization and alsoan unreflected portion 128 of the third transmitted signal 120.

At step 920, the fourth signal 120 is transmitted at the secondpolarization, which is the same polarization as the third signal 120.

At step 924, the portion of the fourth signal 120 travelling through thesample material 118 is reflected at a second reflecting property. Forexample, the fourth signal 120 is reflected by the variable reflector106 that has been adjusted to a second reflectivity different from thefirst reflectivity reflecting the third signal. For example, thevariable reflector 106 is adjusted to the second reflectivity afterreflecting the third signal 120 and prior to reflecting the fourthsignal 120. Due to the reflecting, the amplitude of the fourth reflectedsignal 126 can be different from the fourth signal 120. The amplitude ofthe fourth reflected signal 126 is also different from the amplitude ofthe third reflected signal 126, while the polarization of the fourthreflected signal 126 is the same as the polarization of the thirdreflected signal 126.

At step 928, the fourth received signal is received. For example, thefourth received signal is received by the receiving element 114 ofreceiver 104. The fourth received signal includes the first reflectedsignal 126 that traveled through the sample material 118 with thedefined second polarization and also an unreflected portion 128 of thethird transmitted signal 120. The third received signal 130 and thefourth received signal 130 can be used to determine a physical propertyfor a second direction corresponding to the second defined polarizationof the third and fourth exciting waveform signals 120 and 120.

It will be understood that the first polarization signals can beprocessed in a manner similar to the scalar property determinationdescribed herein to characterize by a first element of a tensor materialproperty and the second differing polarization signals can be processedto characterize by a second element of a tensor material property. Thisis in contrast to determination of sample material 118 properties thatare direction-independent, wherein the received signals can becharacterized by a scalar, and characterization of a signal direction isnot necessary.

Anisotropic properties of the sample material 118 can be determinedbased on direction-dependent properties. For example, properties of thesample material 118 in a first direction corresponding to the firstpolarization of the signal 120 can be determined from analysis of thefirst and second received signals for the first polarization. Similarly,properties of the sample material 118 in a second polarization directioncorresponding to the polarization can be determined from analysis of thethird and fourth received signals with the differing secondpolarization.

According to another exemplary embodiment, the variable reflector 106has adjustable directional reflectivity and can be adjusted to reflectsignals in a selected range of polarizations. The variable reflector 106can be adjusted to reflect in one instance signals having a firstpolarization and in another instance signals having a secondpolarization. For example, the first polarization is orthogonal to thesecond polarization. For example, the variable reflector 106 can be areflector 106 having differently oriented and independently controllablereflecting elements. Alternatively, the variable reflector 106 can bereflector 106 having a rotatable reflecting face.

Where the variable reflector 106 is field direction dependent and can beadjusted to reflected signals in a selected range of polarizations, thetransmitting element 110 can be field direction independent. Thetransmitting element 110 can emit signals in a large range ofpolarizations. For example, the transmitting element 110 can emit asignal having mixed polarization meaning that the emitted signal alwayscontains field components that are not aligned with the variablereflector directional character.

Referring back to FIG. 6, when carrying out the method 900 according tovarious exemplary embodiments using an adjustable direction dependentvariable reflector 106, at step 904 the first signal 120 is transmittedwith a mixed polarization.

At step 908, the portion of the first signal 120 travelling through thesample material 118 is reflected at the variable reflector 106 such thatonly the portion of the first signal 120 having a polarization alignedwith the first direction of the variable reflector is reflected with afirst reflectivity. For example, the variable reflector 106 can modulatethe reflectivity of the portion of the first signal having itspolarization aligned with the variable reflector direction.

At step 912, the first received signal is received. For example, thefirst received signal is received by the receiving element 114 ofreceiver 104. The first received signal includes the first reflectedsignal 126 that traveled through the sample material 118 and also anunreflected portion 128 of the first transmitted signal 120.

At step 920, the second signal 120 is transmitted with the same mixedpolarization as the first signal.

At step 924, the portion of the second signal 120 travelling through thesample material 118 is reflected at the variable reflector 106 such thatonly the portion of the second signal 120 having a polarization alignedwith the first direction of the variable reflector is reflected with asecond reflectivity. The variable reflector 106 can further modulate thereflectivity of the portion of the second signal 120.

At step 928, the second received signal is received. For example, thesecond received signal is received by the receiving element 114 ofreceiver 104. The second received signal includes the second reflectedsignal 126 that traveled through the sample material 118 and also anunreflected portion 128 of the second transmitted signal 120.

Continuing with FIG. 6, the method 900 can be carried out a second time,wherein a third signal and a fourth signal are transmitted and thevariable reflector 106 is adjusted such that it only reflects signalshaving a second polarization. The second polarization is different fromthe first polarization, and in some cases can be orthogonal to the firstpolarization.

At step 904 a third signal 120 is transmitted with a mixed polarization.

At step 908, the portion of the third signal 120 travelling through thesample material 118 is reflected at the variable reflector 106 such thatonly the portion of the third signal 120 having a polarization alignedwith the second direction of the variable reflector is reflected with afirst reflectivity. For example, the variable reflector 106 can modulatethe reflectivity of the portion of the third signal having itspolarization aligned with the variable reflector direction.

At step 912, the third received signal is received. For example, thethird received signal is received by the receiving element 114 ofreceiver 104. The third received signal includes the first reflectedsignal 126 that traveled through the sample material 118 and also anunreflected portion 128 of the third transmitted signal 120.

At step 920, the fourth signal 120 is transmitted with the same mixedpolarization as the third signal.

At step 924, the portion of the second signal 120 travelling through thesample material 118 is reflected at the variable reflector 106 such thatonly the portion of the fourth signal 120 having a polarization alignedwith the second direction of the variable reflector is reflected with asecond reflectivity. For example, the variable reflector 106 can furthermodulate the reflectivity of the portion of the fourth signal 120.

At step 928, the fourth received signal is received. For example, thefourth received signal is received by the receiving element 114 ofreceiver 104. The fourth received signal includes the fourth reflectedsignal 126 that traveled through the sample material 118 and also anunreflected portion 128 of the fourth transmitted signal 120.

It will be understood that the first reflector direction signals can beprocessed in a manner similar to the scalar property determination tocharacterize by a first element of a tensor material property and thesecond reflector direction signals can be processed to characterize by asecond element of a tensor material property. This is in contrast todetermination of sample material 118 properties that aredirection-independent, wherein the received signals can be characterizedby a scalar, and characterization of a signal direction is notnecessary.

Anisotropic properties of the sample material 118 can be determinedbased on direction-dependent reflector properties For example,properties of the sample material 118 in a first direction correspondingto the polarization of the signal 120 aligned with the first reflectordirection can be determined from analysis of the first and secondreceived signals for the first reflector direction. Similarly,properties of the sample material 118 in a second polarization directioncorresponding to the polarization of the signal 120 aligned with thesecond reflector direction can be determined from analysis of the thirdand fourth received signals for the second reflector direction.

Those skilled in the art of vector and tensor analysis will recognizethat a number of variations on these base cases can be developed thataccomplish the measurement objective.

Determining a Frequency-Dependent Property of the Material

According to one exemplary embodiment, method 900 may be carried out toallow determination of a frequency dependent property of the samplematerial 118. The first signal 120 is transmitted at step 904 and issubsequently reflected at step 908 such that the first received signalhas analyzable frequency characteristics. Similarly, the second signal120 is transmitted at step 920 and is subsequently reflected at step 924such that the second received signal also has analyzable frequencycharacteristics.

According to one exemplary embodiment, the signal generator 112 of thetransmitter 100 can emit an excitation signal having a non-zeroamplitude over a wide range of frequencies. For example, an excitationsignal 120 emitted from the transmitter 100 has substantially the sameamplitude over a determined frequency range. Importantly, the frequencyresponse of the emitted excitation signal 120 is known. For example, theemitted excitation signal can be formed by simultaneously emitting aplurality of sinusoidal signals, a swept chirp over a range offrequencies, transmission of a wideband, and other known methods ofsending a wideband signal.

The variable reflector 106 can be frequency dependent and can beadjusted in order to have a test reflectivity in a test frequency rangecorresponding to a first frequency range. The test reflectivity in thetest frequency range is differentiable from the reflectivity of thevariable reflector 106 at frequencies outside the test frequency range.For example, the test reflectivity in the test frequency range can beincreased and decreased while the reflectivity at frequencies outsidethe test frequency range remains fixed. By having differentreflectivities in different frequency ranges, it is possible to analyzefrequency dependent properties of the sample material 118. For example,where the test reflectivity in the test frequency range is greater thanthe reflectivity of the reflector 106 at frequencies outside the testfrequency range, it is possible to analyze the properties of the samplematerial 118 in that test frequency range corresponding to the firstfrequency range.

The variable reflector 106 can be further adjusted to adjust boundariesof the test frequency range. For example the variable reflector 106 canbe adjusted so that the test frequency range corresponds to a secondfrequency range that is different from the first frequency range. Forexample the second frequency range can slightly overlap with the firstfrequency. Adjusting the boundaries of the test range allows theanalysis of the frequency dependent properties of the sample material118 on a different range of frequencies.

Referring back to FIG. 6, when carrying out the method 900 according tovarious exemplary embodiments using an adjustable frequency dependentvariable reflector 106, at step 904 a first signal 120 having a non-zeroamplitude over a wide of range of frequencies is transmitted.

At step 908, the portion of the first signal 120 travelling through thesample material 118 is reflected at the variable reflector 106. Thevariable reflector 106 is adjusted so that it has the test reflectivityin the test frequency range corresponding to a first frequency range. Atleast a portion of the first frequency range is a sub-range of the rangeof frequencies where the first signal 120 has non-zero amplitude. As aresult, the first reflected signal 126 has distinguishablecharacteristics in the frequency range corresponding to the firstfrequency range. For example, where the test reflectivity in the testfrequency range is greater than the reflectivity in frequency rangesoutside the test frequency range and the first signal 120 has asubstantially constant amplitude over its own sub-range, the firstreflected signal 126 should have a greater amplitude in the frequencyrange corresponding to the first frequency range. It will be appreciatedthat reflecting the first signal 120 at the test reflectivity in thetest frequency range corresponding to the first frequency range has theeffect of isolating signals limited to the first frequency range.

At step 912, the first received signal is received. For example, thefirst received signal 130 is received by the receiving element 114 ofreceiver 104. The first received signal 130 includes the first reflectedsignal 126 that traveled through the sample material 118 and also anunreflected portion 128 of the first transmitted signal 120.

At step 920, a second signal 120 having a nonzero amplitude over a widerange of frequencies is transmitted. For example, the second signal issubstantially the same as the first signal 120, namely that the secondsignal 120 also has a non-zero amplitude in the same wide range offrequencies of the first signal 120.

At step 924, the portion of the second signal 120 travelling through thesample material 118 is reflected at the variable reflector 106. Forexample, before reflecting the second signal 120, the variable reflector106 is adjusted so that it has the test reflectivity in its testfrequency range corresponding to a second frequency range that isdifferent from the first frequency range. At least a portion of thesecond frequency range is a sub-range of the range of frequencies wherethe second signal 120 has non-zero amplitude. As a result, the secondreflected signal 126 has distinguishable characteristics in thefrequency range corresponding to the second frequency range. Forexample, where the test reflectivity in the test frequency range isgreater than the reflectivity in frequency ranges outside the testfrequency range and the second signal 120 has a substantially constantamplitude over its own sub-range, the second reflected signal 126 shouldhave a greater amplitude in the frequency range corresponding to thesecond frequency range. It will be appreciated that reflecting thesecond signal 120 at the test reflectivity in the test frequency rangecorresponding to the second frequency range has the effect of isolatingsignals limited to the second frequency range.

At step 928, the second received signal is received. For example, thesecond received signal is received by the receiving element 114 ofreceiver 104. The second received signal includes the second reflectedsignal 126 that traveled through the sample material 118 and also anunreflected portion 128 of the second transmitted signal 120.

Since first reflected signal 126 has distinguishable characteristics inthe first frequency range, the first received signal can be analyzed todetermine properties of the sample material 118 limited to the firstfrequency range. Similarly, since the second reflected signal 126 hasdistinguishable characteristics in the second frequency range, thesecond received signal can be analyzed to determined properties of thesample material 118 limited to the second frequency range.

Steps 904 to 912 of method 900 can be repeated, wherein the variablereflector 106 is adjusted so that the test frequency range correspondsto different ranges of frequencies. This allows for determination ofproperties of the sample material 118 over multiple ranges offrequencies.

According to one exemplary embodiment, differently spatially locatedreflecting surfaces 124 are used for reflecting transmitted signals 120.The variable reflector 106 can have a plurality of reflecting surfaces124 that can be simultaneously mounted onto a surface of the samplematerial 118. When mounted on the surface of the sample material 118,each reflecting surface 124 of the variable reflector covers a differentlocation of the surface of the sample material. Additionally, thetransmitter 102 can have more than one transmitting element 110 and thereceiver 104 can have more than one receiving element 114. For example,the plurality of transmitting element 110 can be simultaneously mountedonto the surface of the sample material 118 and can be positioned atdifferent locations of the surface of the sample material. For example,the plurality of receiving element 114 can be simultaneously mountedonto the surface of the sample material 118 and can be positioned atdifferent locations of the surface of the sample material. The pluralityof differently spatially located reflecting surfaces 124 can be used toexamine the spatial variation of at least one property of the samplematerial 118.

According to various exemplary embodiments, method 900 for measuring aproperty of a sample material 118 can be repeated over a duration oftime. Where the sample material 118 is a fluid or loose solid, themethod 900 and 1000 can be repeated in order to monitor the variabilityof the sample material 118 as a function of time.

According to various exemplary embodiments, method 900 for measuring aproperty of a sample material 118 can be repeated over an extendedduration of time. For example, a sample material 118, including somestatic materials, can have time-varying properties. For example, soilsbeing wetted or drained (rain fall followed by dry weather) and curingof concrete have time-varying properties. Accordingly methods 900 and1000 can be repeated over the extended duration of time in order tomonitor the variation of the property as a function of time.

Referring now to FIG. 8, therein illustrated is a schematic diagram of amethod 1100 for determining a property of a sample material 118 based onknown properties of a reference material.

At step 1104, the sample material is provided. The sample material 118is further probed according to the method 900. A first signal 120 and asecond signal 120 are transmitted at steps 904 and 908. A portion of thefirst signal 120 is reflected at a first reflecting property at step912. A portion of the second signal 120 is reflected at a secondreflecting property at step 920. A first received signal that includesthe first reflected signal 126 and a second received signal thatincludes the second reflected signal 126 are received at step 924 andstep 928 respectively.

At step 1108, the reference material is provided. The reference materialhas known properties. Furthermore, some of the dimensions of thereference material should be substantially the same as the dimensions ofthe sample material 118. The signal path traveled by a signal betweenthe transmitter 102, variable reflector 106 and receiver 104 through thereference material should be equivalent to the signal path 122 traveledby a signal through the sample material 118. The reference material isfurther probed according to the method 900. For example, a third signalis transmitted into the reference material at step 904 and fourth signalis transmitted into the reference material at step 908. The third signalis reflected at a third reflecting property at step 912. The thirdreflecting property can be the same as, or different from, the firstreflecting property. The fourth signal is reflected at fourth reflectingproperty at step 920. The fourth reflecting property can be the same as,or different from, the second reflecting property. A third receivedsignal that includes the third reflected signal and a fourth receivedsignal that includes the fourth reflected signal are received at step924 and step 928 respectively.

At step 1112, the first received signal and the second received signalreceived from probing the sample material 118 are compared with thethird received signal and the fourth received signal received fromprobing the reference material. The comparison is carried out in orderto determine a property of the sample material based on at least oneknown property of the reference material. For example, the correlationcan be carried out by the signal processor of the measurement system100.

According to various exemplary embodiments, the comparison of step 1112can be carried out in order to determine a velocity of the transmittedsignal through the sample material 118. The comparison of step 1112 canbe carried out in order to also determine an attenuation factor of thesample material.

As previously described herein, a difference between the first receivedsignal and a second received signal can be calculated in order toisolate the first reflected signal 126 and the second reflected signal126 that traveled through the sample material 118. A plurality of firstsignals and second signals can be transmitted through the samplematerial 118 and the calculated difference can be averaged. Thedifference of the first received signal and the second received signalcan be represented as:

o _(j) ¹ −o _(k) ¹

=(M _(j) ¹ −M _(k) ¹)w(t−T _(a) ¹)

Similarly a difference of the third received signal and the fourthreceived signal can be calculated in order to isolate the thirdreflected signal and the fourth reflected signal that traveled throughthe reference material. A plurality of third signals and fourth signalscan be transmitted through the reference material and the calculateddifference can be averaged. The difference of the third received signaland the fourth received signal can be represented as:

o _(j) ^(R) −o _(k) ^(R)

=(M _(j) ^(R) −M _(k) ^(R))w(t−T _(a) ^(R))

Where a velocity v_(R) of the signal through the reference material canbe known based on known properties of the reference material, thevelocity v_(a) of the sample material can be determined based on thetravel time T_(a) ¹ of a signal over the reflected signal path 122through sample material 118 and the travel time T_(a) ^(R) of a signalover an equivalent path through the reference material. For example, thevelocity v_(a) can be determined according to the equation:

$v_{a} = {v_{R}\frac{T_{a}^{R}}{T_{a}^{1}}}$

The sample material 118 and the reference material can have differentattenuation factors along the reflected signal path 122. The factor ofchange in amplitude of a signal traveling through the sample material118 over the reflected signal path 122 can be represented as e^(−∝) ¹^(L) ^(a) where ∝₁ is the attenuation of the sample material 118 andL_(a) is the length of the signal path 122. Similarly the factor ofchange in amplitude of a signal traveling through the reference materialover the reflected signal path 122 can be represented as e^(−∝) ^(R)^(L) ^(a) where ∝_(R) is the attenuation of the reference material andL_(a) is the length of the signal path 122. It will be appreciated thatattenuation can be represented as occurring exponentially due to energydissipation in material and that the amplitude will fall off as afunction of path length.

The ratio of the difference between the first received signal and thesecond received signal with the difference between the third receivedsignal and the fourth can be represented as:

$\frac{\left( {M_{j}^{1} - M_{k}^{1}} \right)}{\left( {M_{j}^{R} - M_{k}^{R}} \right)} = {C\frac{^{- {\propto_{1}L_{a}}}}{^{- {\propto_{R}L_{a}}}}}$

The C factor reflects the fact that the material change may change theintrinsic element coupling of energy to and from the material. Withproper design, C˜1 can be achieved. For example purposes, C is hereinunderstood as equaling 1. The observed signal will depend on thematerial attenuation and changes in modulated reflector response.

Taking the natural logarithm of numerator and the denominator of theequation:

$\frac{\left( {M_{j}^{1} - M_{k}^{1}} \right)}{\left( {M_{j}^{R} - M_{k}^{R}} \right)} = \frac{^{- {\propto_{1}L_{a}}}}{^{- {\propto_{R}L_{a}}}}$

provides the relationship:

$\frac{\ln \left( {M_{j}^{1} - M_{k}^{1}} \right)}{\ln \left( {M_{j}^{R} - M_{k}^{R}} \right)} = \frac{\propto_{1}}{\propto_{R}}$

attenuation ∝₁ of the sample material 118 can then be written in termsof the reference sample attenuation and the amplitude of the modulationratio:

$\propto_{1}{= {\propto_{R}\frac{\ln \left( {M_{j}^{1} - M_{k}^{1}} \right)}{\ln \left( {M_{j}^{R} - M_{k}^{R}} \right)}}}$

Referring now to FIG. 9, therein illustrated is a schematic diagram ofan unsynchronized method 1200 for determining a property of a samplematerial 118 according to various exemplary embodiments. Advantageously,the method 1200 does not require synchronization between the time ofsending a signal 120 from the transmitter 102 and the time of adjustinga reflecting property of the variable reflector 106.

At step 1204, a plurality of signals 120 is transmitted into the samplematerial 118. The signals 120 are transmitted sequentially in time andover a duration that is substantially longer than the amount of timetaken to adjust the reflecting property of the variable reflector 106.

At step 1208, during the duration of time in which the plurality ofsignals 120 is being transmitted from the transmitter 102, thereflecting property of the variable reflector 106 is adjusted at leastonce. The variable reflector 106 is adjusted at least from a firstreflecting property to a second reflecting property. According to someexemplary embodiments, the variable reflector 106 can be furtheradjusted from the second reflecting property back to the firstreflecting property. The adjusting of the reflecting property of thevariable reflector 106 while the transmitting of the signals 120 isongoing has the effect that a first subset of the plurality of signalsare reflected at the first reflecting property and a second subset ofthe plurality of the transmitted signals 120 are reflected at the secondreflecting property.

At step 1212, a plurality of the reflected signals 126 are received atthe receiver 104. The reflected signals 126 include signals reflected atthe first reflecting property and signals reflected at the secondreflecting property.

For example, step 1204 and step 1212 can form a loop, wherein in eachcycle of the loop a signal 120 is transmitted at step 1204, and thecorresponding reflected signal 126 is received at the receiver 102 atstep 1212. For example, two adjacent transmissions of signals 120 atstep 1204 of two cycles of the loop can be sufficiently spaced apart intime such that the unreflected portion 128 of the later transmittedsignal does not interfere with the reflected portion 126 of the earliertransmitted signal. The time between the beginning of a transmission ofsignal 120 at step 1204 and a completion of the reception of thecorresponding received signal at step 1212 defines one observationo_(j)(t) made by the receiver 102. It will be appreciated that oneobservation is made per cycle of the loop of steps 1204 and 1212. As aresult, a plurality of observations o_(j)(t) are made.

Step 1208 is carried out during the repeating of the loop formed by step1204 and 1212, but the timing of adjusting the variable reflector 106 atstep 1208 is not synchronized with any individual transmission of thesignal 120 at step 1204 or any individual reception of the receivedsignal at step 1208. Accordingly, the variable reflector 106 can beunderstood as being asynchronous with the transmitter 102 and receiver104.

At step 1216, the plurality of received signals are sorted based onwhether an individual signal 120 was reflected at the first reflectingproperty or at the second reflecting property. For example, where thereceived signals are received by the receiver 104 as a plurality ofobservations o_(j)(t), an average o_(a)(t) of the observations iscalculated:

${o_{a}(t)} = {\frac{1}{N}{\sum\limits_{j = 1}^{N}\; {o_{j}(t)}}}$

For an individual observation o_(j)(t) corresponding to one of thereceived signals, a difference o_(j)′(t) is calculated according to:

o _(j)′(t)=o _(j)(t)−o _(a)(t)

Since only the portion of the received corresponding to the reflectedsignal 126 and noise is present in the difference o_(j)′(t), thedifference can be expressed as:

${o_{j}^{\prime}(t)} = {{{\pm \frac{\left( {M_{2} - M_{1}} \right)}{2}}{w\left( {t - T_{a}} \right)}} + {n_{j}(t)}}$

wherein the ± signs reflects the fact that the difference can correspondto either a signal 120 reflected at the first reflecting property or thesecond reflecting property. Assuming n_(j)(t) is small, then a receivedsignal can be sorted based on the individually determined differenceso_(j)′(t) into two groups depending on the sign of the dominant event.

g _(j) ⁺(t)=o _(j)′(t) if sign positive j=1,N ₊

wherein g_(j) ⁺(t) corresponds to signals reflected at the firstreflecting property,

g _(j) ⁻(t)=o _(j)′(t) if sign negative j=1,N ⁻

wherein g_(j) ⁻(t) corresponds to signals reflected at the secondreflecting property and

g _(j) ^(?)(t)=o _(j)′(t) if sign indeterminate j=1,N _(?)

wherein g_(j) ^(?)(t) corresponds to signals that does not allow a cleardetermination of how the signal 120 was reflected. An average of thesorted signals determined as being reflected at the first reflectingproperty is computed according to:

${\langle{g^{+}(t)}\rangle} = {\frac{1}{N_{+}}{\sum\limits_{j = 1}^{N_{+}}\; {g_{j}^{+}(t)}}}$

An average of the stored signals determined as being reflected at thesecond reflecting property is computed according to:

${\langle{g^{-}(t)}\rangle} = {\frac{1}{N_{-}}{\sum\limits_{j = 1}^{N_{-}}\; {g_{j}^{-}(t)}}}$

A difference of the average of the signals reflected at the firstreflecting property and the average of the signals reflected at thesecond reflecting property can be computed according to:

g ⁺(t)

−

g ⁻(t)

=(M ₂ −M ₁)w(t−T _(a))

It will be appreciated that this equation is similar to the isolatedfirst and second reflected signals calculated at steps 1004 of method1000. Various properties of the sample material 118 can then bedetermined according to methods described herein. For example, anelectrical permittivity of the sample material 118 can be determinedbased on the time delay T_(a) and a path length L_(a).

The steps of method 1200 for determining a property of the material canbe performed as part of step 1104 of probing a sample material 118 ofmethod 1100. The steps of method 1200 can also be performed as part ofstep 1108 of probing a reference material of method 1100. The first andsecond received signals determined at step 1104 of probing the samplematerial 118 and the isolated third and fourth received signalsdetermined from step 1108 of probing the reference material can then becorrelated at step 1112 in order to determine one or more properties ofthe sample material 118. For example, a permittivity of the samplematerial 118 and/or an attenuation factor of the sample material 118 canbe calculated.

While various exemplary embodiments have been described with referenceto reflecting transmitted signals 120 at a first reflecting property anda second reflecting property, it will be understood that transmittedsignals 120 can be further reflected at additional reflectingproperties. Signals received from being reflected at the additionalreflecting properties can be further used to determine one or moreproperties of the sample material 118. Exemplary methods describedherein can be further adapted for the reflecting of transmitted signals120 at additional reflecting properties.

According to various exemplary embodiments, at least one transmitter102, at least one receiver 104, and at least one variable reflector 106can be provided as a kit As described elsewhere herein, the transmitter102 can transmit a plurality of signals into a material to be measured,the variable reflector can reflect signals propagating through thematerial to be measured at at least a first reflecting property and asecond reflecting property, and the receiver can receive a plurality ofsignals propagating through the material to be measured. For example,the transmitter 102, receiver 104 and variable reflector 106 can betransported separately, and assembled on-site to form the measurementsystem 100 described herein. For example, the kit 1300 can furtherinclude the controller 108 for controlling the transmitter 102 and thereceiver 104, and optionally the variable reflector 106. Alternatively,one or more of the transmitter 102, receiver 104, and variable reflector106 can connect with an external controller, such as a computer deviceor handheld device in order to receive various control signals. Forexample, the kit 1300 can further include a non-transitorycomputer-readable medium upon which a plurality of instructions arestored for carrying out various exemplary methods described herein. Theplurality of instructions include at least instructions for controllingthe at least one transmitter 102 to transmit the first signal;controlling the at least one transmitter 102 to transmit the secondsignal; controlling the at least one variable reflector 106 to adjustthe reflecting property of the reflected between the first reflectingproperty and the second reflecting property; and isolating the firstreceived signal and the second received signal.

Referring now to FIG. 10, therein illustrated a perspective view of anexemplary packaged measurement system 1300 that is ready for field use.The packaged measurement system 1300 includes a support frame 1304 forsupporting a sample material 118 to be measured. The packagedmeasurement system 1300 may further include a container 1308 for holdingthe sample material 118 (ex: where the sample material 118 is a fluid orhas a plurality of discrete pieces). The container 1308 is formed of amaterial that is permeable to electromagnetic signals and which hasknown properties. The support member 1304 provides for mounting theretoa transmitter 102 and a receiver 104 such that signals transmitted fromthe transmitter 102 and received at the receiver 104 substantially onlytravel through the sample material 118 supported by the support frame1304. The support member 1304 further provides mounting thereto areflector 106 at a position opposite the mounted transmitter 102 andreceiver 104. In this way, signals transmitted from the transmitter 102travel through the sample material 118 being supported and is reflectedby the reflector 106. Signals reflected by the reflector 106 furthertravel through the sample material 118 to be received at the receiver104.

According to the example illustrated in FIG. 10, the transmitter 103 andreceiver 104 are packaged within a single transducer unit 1312. Forexample, the single transducer unit 1312 can be a transducer unit usedin ground penetrating radar (GPR) applications. For example, the singletransducer unit can be the TR1000™ transducer provided by Sensor andSoftware.

An input/output port 1316 of the transducer unit 1312 may be furtherconnected to an input/output device 1320, which may be laptop, tablet,smartphone, or other suitable devices known in the art. For example, thetransducer 1312 communicates with the input/output device 1320 via aninterface device 1324. For example the interface device 1324 may be aSPIDAR™ network interface controller provided by Sensor and Software.

The transducer unit 1312 may provide functions of the controller 108 asdescribed herein. Alternatively, the input/output device 1320 mayprovide functions of the controller 108. Alternatively, functionsprovided by controller 108 of the measurement system may be share and/orsplit amount the transducer unit 1312 and the input/output device 1320.

The packaged measurement system 1300 may further include a power supply1328. The power supply 1328 may be a portable battery for portabledeployment of the packaged measurement system 1320.

According to some exemplary embodiments where the mounted reflector 106is a controllable variable reflector, the input/output device 1320 maybe further connected to the variable reflector 106 to selectively changereflecting properties of the variable reflector 106.

Referring now to FIG. 11, therein illustrated is a perspective view ofan alternative exemplary packaged measurement system 1300′ that is readyfor field use. The alternative packaged measurement system 1300′ isprovided with the transmitter 102 and receiver 104 enclosed within anenclosure 1332 already mounted onto the support frame 1304 opposite thereflector 106. The interface device 1324 providing communication betweenthe input/output device 1320 and the variable reflector 106 may also beenclosed within the enclosure 1332. Accordingly the enclosure 1332presents a first input/output port for connection to the input/outputdevice, a second port for connection with a power supply and, whereapplicable, a third port for connection with a variable reflector 106for selectively adjusting reflecting properties thereof.

Referring now to FIG. 12, therein illustrated is an exemplary elongatedconductive element 1400. The elongated conductive element 1400 can beenergized by an incident electromagnetic field. “Energizing a conductiveelement” or variations thereof herein refers to the conductive elementreceiving energy from the electromagnetic field and having a flow ofcurrent through it as a result of receiving that energy.

The elongated conductive element 1400 provided in various exemplaryembodiments is selected to have a length 1404 that is substantially lessthan characterizing features of incident electromagnetic signals thatare expected to energize the elongated conductive element 1400. Inparticular, the length 1404 of the elongated conductive element 1400 isshorter than a pulse duration or a wavelength of expected incidentelectromagnetic signals. The elongated conductive element further has ashape wherein its length 1404 is substantially greater than itscross-sectional dimension (width 1408 and height 1412). Due to theelongated shape of the conductive element 1400, an incidentelectromagnetic signal causes a current to flow in the direction of thelengths of the conductive element 1400 while the current in otherdirections are negligible. Furthermore, due to the elongated shape ofthe conductive element 1400, the conductive element 1400 issubstantially energized by the directional component of the incidentelectromagnetic signal that is substantially parallel to the orientationof the length of the conductive element 1400. Components of the incidentelectromagnetic signal in other directions do not have a significantenergizing effect on the conductive element 1400.

When there is electrical current flow through the conductive element1400, the conductive element 1400 creates a scattered electromagneticfield in the space surrounding the conductive element 1400. The amountof scattering can be represented by the following expressions describedin [1]:

TABLE 5-1 Fields of a Short Electric Dipole Component General ExpressionFar Field Quasi-Stationary E_(r)$\frac{\lbrack I\rbrack L\mspace{14mu} \cos \mspace{14mu} \theta}{2{\pi ɛ}_{0}}\left( {\frac{1}{{cr}^{2}} + \frac{1}{j\; \omega \; r^{3}}} \right)$0$\frac{q_{0}\mspace{14mu} L\mspace{14mu} \cos \mspace{20mu} \theta}{2{\pi ɛ}_{0}r^{3}}$E_(θ)$\frac{\lbrack I\rbrack L\mspace{14mu} \sin \mspace{14mu} \theta}{4{\pi ɛ}_{0}}\left( {\frac{j\; \omega}{c^{2}r} + \frac{1}{{cr}^{2}} + \frac{1}{j\; \omega \; r^{3}}} \right)$$\frac{\lbrack I\rbrack {Lj}\; \omega \mspace{14mu} \sin \mspace{14mu} \theta}{4{\pi ɛ}_{0}c^{2}r} = {\frac{j\; 60\; {\pi \lbrack I\rbrack}\mspace{14mu} \sin \; \theta}{r}\frac{L}{\lambda}}$$\frac{q_{0}\mspace{14mu} L\mspace{14mu} \sin \mspace{20mu} \theta}{4{\pi ɛ}_{0}r^{3}}$H_(φ)$\frac{\lbrack I\rbrack L\mspace{14mu} \sin \mspace{14mu} \theta}{4\pi}\left( {\frac{j\; \omega}{cr} + \frac{1}{\; r^{2}}} \right)$$\frac{\lbrack I\rbrack {Lj}\; \omega \mspace{14mu} \sin \mspace{14mu} \theta}{4{\pi {cr}}} = {\frac{{j\lbrack I\rbrack}\mspace{14mu} \sin \; \theta}{2r}\frac{L}{\lambda}}$$\frac{I_{0}\mspace{14mu} L\mspace{14mu} \sin \mspace{20mu} \theta}{4{\pi r}^{2}}$The restritction applies that r >> L and λ >> L. The quantities in thetable are in SI units, that is, E in volts per meter, H in amperes permeter, I in amperes, r in meter, etc. Three of the field components ofan electric dipole are everywhere zero, that is, E_(φ) = H_(r) = H_(θ) =0wherein I is the current amplitude through the conductive element 1400,L is the length 104 of the current element, r, θ, φ are spherical polarcoordinates with r being the distance of the observation point from thecenter of the conductive element 1400 and θ the angle between the axisof the conductive element 1400 and the radial direction to theobservation point, c is the speed of light vacuum, ω is a frequency ofthe scattered electromagnetic signal.

As a result of an incident electromagnetic signal impinging on theelectrical conductive element 1400 and energizing the conductive element1400, a scattered electromagnetic field is created by the conductiveelement 1400. Where there are no other sources energizing the conductiveelement 1400, the scattered electromagnetic field is caused only by theincident electromagnetic signal energizing the conductive element 1400.Accordingly, properties of the scattered electromagnetic field willdepend only on properties of the incident electromagnetic signal,properties of the conductive element 1400 and properties of the spacesurrounding the conductive element 1400. Where properties of theconductive element 1400 and surrounding space are known, it is possibleto determine characteristics of an incident electromagnetic signal basedon measurement of the scattered signal. Similarly, where properties ofconductive element 1400 and the incident signal are known, it ispossible to determine characteristics of the surrounding space based onmeasurement of the scattered electromagnetic signal.

The energizing and scattering performed by conductive element 1400 canbe understood as reflecting received incident electromagnetic signal toproduce a scattered (reflected) electromagnetic signal. The relationshipbetween the incident electromagnetic signal and the reflected scatteredelectromagnetic field can be understood as a reflecting property of theconductive element 1400.

According to various exemplary embodiments, the conductive element canbe formed of a metallic wire section or of metalized deposits on adielectric (insulating) substrate.

Referring now to FIG. 13, therein illustrated is a plan view of anexemplary interconnection 1500 of a plurality of conductive elements1400 being interconnected by a plurality of variable impedance junctionelements 1504. According to the example shown in FIG. 13, six conductiveelements denoted as first conductive element 1400 a, second conductiveelement 1400 b, third conductive element 1400 c, fourth conductiveelement 1400 d, fifth conductive element 1400 e and sixth conductiveelement 1400 g are provided. According to the example shown in FIG. 13,five conductive elements denoted as first junction 1504 a, secondjunction 1504 b, third junction 1504 c, fourth junction 1504 d, andfifth junction 1504 e are provided. The conductive elements 1400 a-1400g are shown as being linearly arranged and positioned end to end. Eachjunction element 1504 a-204 f interconnects two adjacently positionedconductive elements 1400. While FIG. 13 illustrates an exemplaryarrangement having six conductive elements 1400 and five junctionelements 1504, it will be understood that any number of conductiveelements 1400 and corresponding junction elements 1504 interconnectingthe conductive elements 1400 may be used.

According to one exemplary embodiment, the junction elements 1504 arecontrollable to be varied between an insulating state and a conductingstate. In the conducting state, a junction element 1504 provides aconducting electrical connection between the two conductive elements1400 joined to the junction element 1504 to allow flow of electricitybetween the two conductive elements 1400. In the insulating state, thejunction element 1504 electrically separates the two conductive elements1400 joined to the junction element 208 such that electricity cannotflow between the two conductive elements 1400. For example, the junctionelements 1504 can be diodes that can be toggled between an insulatingstate and a conducting state through application of a bias voltage.Alternatively, the junction elements 1504 can be photosensitive diodesthat move between the insulating state and the conducting statedepending on an amount of light incident upon the diodes.

Referring now to FIG. 14, therein illustrated is a schematic electricalcircuit diagram of the connection of conductive elements 1400 andjunction elements 1504. The conductive elements 1400 a, 1400 b, 1400 c,1400 d, 1400 e, 1400 f can be represented by a plurality of electricallines having respective line impedances 1508 a, 1508 b, 1508 c, 1508 d,1508 e, and 1508 f. These lines are interconnected by diodes 1512 a,1512 b, 1512 c, 1512 d, and 1512 e which respectively represent thejunction elements 1504 a, 1504 b, 1504 c, 1504 d, and 1504 e. It will beunderstood that applying a positive bias voltage over a diode will causeconducting of electricity between two electrical lines 1508 connected tothe diode. Conversely, applying a negative bias voltage at diode 1512will cause two electrical lines 1508 connected to a diode 1512 to beelectrically insulated. A diode 1512 is in the conducting state when apositive bias voltage is applied and it will be in the insulating statewhen a negative bias voltage is applied or no voltage is applied.

It will be appreciated that by providing electrical connection betweenthe conductive elements 1400, the junction elements 1504 combine theconductive elements 1400 to form one or more combination conductiveelements. The combination of conductive elements have lengths that aregreater than the lengths 1404 of the individual conductive elements. Forexample, when each of the junction elements 1504 a to 1504 e ofarrangement 1500 are in the conducting state, a combination conductiveelement is formed having a length equal to the combined lengths of thesix conductive elements 1504 a to 1504 e.

Further control of the junction elements 1504 allows the formation ofdifferent numbers of combination conductive elements having differentlengths. For example, FIG. 15 illustrates two combination conductiveelements 1516 a and 1516 b. First conductive elements 1516 a is formedof first conductive element 1400 a, second conductive element 1400 b,and third conductive element 1400 c being connected by junction elements1504 a and 1504 b in the conducting state. Second conductive element1516 b is formed of fourth conductive element 1400 d, fifth conductiveelement 1400 e and sixth conductive element 1400 f being connected byjunction elements 1504 d and 1504 e in the conducting state. Thirdjunction element 1504 c is controlled to be in the insulating state toseparate the first combination conductive element 1516 a from the secondcombination conductive element 216 b.

For example, FIG. 16 illustrates another combination wherein threecombination conductive elements 1516 c, 1516 d, and 1516 e are formed.Third combination conductive element 1516 c is formed of the firstconductive element 1400 a and second conductive element 1400 b. Fourthcombination conductive element 1516 d is formed of the third conductiveelement 1400 c and the fourth conductive element 1516 d. Fifthconductive element 1516 e is formed of the fifth conductive element 1400e and the sixth conductive element 1400 f. First junction element 1504a, third junction element 1504 c, and fifth junction element 1504 e arecontrolled to be in the conducting state. Second junction element 1504 band fourth junction element 1504 d are controlled to be in theinsulating state.

It will be appreciated that control of the junction elements to vary theconducting state of different junction elements 1504 allows thevariation of the effective lengths of the combination conductiveelements from the conductive elements 1400. It will be furtherappreciated that the length of the combination conductive elements willbe a multiple of the length of a single elongated conductive element1400.

The strength of the current flow in a combination conductive element1516 resulting from energizing by the incident electromagnetic signalwill depend on the lengths of the combination conductive elements 1516formed from the elongated conductive elements 1400. The strength of thescattered electromagnetic signal will also depend on the length of thecombination conductive element 1516. Therefore, control of the variableimpedance junction elements 1504 to vary the length of the combinationconductive elements 216 that are formed provide a way for controllingthe reflecting property of a reflector formed from the conductiveelements 1400. As a result, varying the impedance of the variableimpedance junction elements 1504 also varies the scatteredelectromagnetic signal scattered from the combination conductiveelements. Varying the lengths of the combination conductive element 1516varies frequency-related reflecting property of the reflector.

According to various exemplary embodiments, the junction elements 1504are variable impedance elements that can be adjusted to have a desiredimpedance value within a range of possible impedances. For example, eachjunction element 1504 is a variable resistor. For example, the junctionelement 1504 is a diode or photo diode. According to some exemplaryembodiments, the junction element 1504 is a resistive device that issensitive to heat (thermal), sound (acoustic) or pressure. It will beunderstood that examples of junction elements 1504 provided herein arenot intended to be exhaustive and other suitable elements having anadjustable impedance may be used for the junction element 1504.According to variable exemplary embodiments, the variable impedancejunction elements 1504 can be controlled to be in an insulating statewherein flow of electricity between two conductive elements 1400connected by the junction element 1504 is prevented. The variableimpedance junction elements 1504 can be further controlled to be in aconducting state, wherein when in the conducting state the junctionelement 1504 can be further controlled to have a desired impedance valuewithin the range of possible impedances.

According to some exemplary embodiments, the shift of the junctionelement 1504 between the conducting state and the insulating stateoccurs gradually through a continuous range of impedance values.Alternatively, the shift of the junction element 1504 between theconducting state and the insulating state occurs abruptly between thetwo states.

According to various exemplary embodiments, the impedance of thejunction elements 1504 can vary based on environmental conditions. Forexample, various devices can be used that change electrical propertiesbased on changing environmental conditions such as temperature, light,moisture, pressure. For example, the junction elements are thermistors.

Referring now to FIG. 17, therein illustrated is a schematic electricalcircuit diagram of the connection of conductive elements 1400 andvariable impedance junction elements 1504. The conductive elements 1400a, 1400 b, 1400 c, 1400 d, 1400 e, 1400 f can be represented by aplurality of electrical lines having respective line impedances 1508 a,1508 b, 1508 c, 1508 d, 1508 e, and 1508 f. These lines areinterconnected by variable impedances 1520 a, 1520 b, 1520 c, 1520 d,and 1520 e which respectively represent the variable impedance junctionelements 1504 a, 1504 b, 1504 c, 1504 d, and 1504 e. For example, theimpedance of the junction elements 1504 can be adjusted by applying a DCbias to the ends the combination of conductive elements 1400.Alternatively, a DC bias can be applied to subsections of thecombination of conductive elements 1400. When applying an electricalbias, care should be taken so that an electromagnetic response is notcreated in the conductive elements 1400. Alternatively, temperaturechange or light impinging or pressure or some other mechanism can alsobe used to control the impedance of the junction elements 1504.

Controlling of the junction elements 1504 allows for the combining ofconductive elements 1400 to form one or more combination conductiveelements. As described in relation to FIGS. 15 and 16, controlling thevariable impedance conductive elements 1504 between conducting andinsulating states allows the formation of combination conductiveelements of variable lengths.

Referring now to FIG. 18, therein illustrated are two combinationsconductive elements 216 a and 216. First combination conductive elements216 a is formed of first conductive element 1400 a, second conductiveelement 1400 b, and third conductive element 1400 c being connected byjunction elements 1504 a and 204 b in the conducting state. Secondconductive element 216 b is formed of fourth conductive element 1400 d,fifth conductive element 1400 e and sixth conductive element 1400 fbeing connected by junction elements 1504 d and 204 e in the conductingstate. Third junction element 1504 c is controlled to be in theinsulating state to separate the first combination conductive element216 a from the second combination conductive element 216 b.

In addition to controlling the first junction element 1504 a, secondjunction element 1504 b, fourth junction element 1504 d and fifthjunction element 1504 e to the conducting state, each of these junctionelement 1504 can be further controlled to a desired impedance value,which results in the varying of an effective impedance of thecombination conductive elements formed from the conductive elements1400. For example, effective impedance 1524 a for the first combinationconductive element 1516 a is the sum of the impedance values of thefirst line impedance 1508 a, first variable impedance 1520 a, secondline impedance 1508 b, second variable impedance 1520 b, and third lineimpedance 1508 c. For example, effective impedance 1524 b for the secondcombination conductive element 1516 b is the sum of the impedance valuesof the fourth line impedance 1508 d, fourth variable impedance 1520 d,fifth line impedance 1508 e, fifth variable impedance 1520 e, and sixthline impedance 1508 f. By varying both the length and the impedance ofthe combination conductive elements that are formed from the conductiveelements 1400, effective impedance per unit lengths for the formedcombination conductive elements can be achieved.

The strength of the current flow in a combination conductive element1516 resulting from energizing by the incident electromagnetic signalwill depend on the impedance of the combination conductive elements 1516formed from the elongated conductive elements 1400. It will beappreciated that the scattered electromagnetic signal will also dependon the impedance of the combination conductive element 1516. Therefore,control of the variable impedance junction elements 1504 to vary theimpedance per unit length of the combination conductive elements 1516that are formed provides a way for controlling the reflecting propertyof a reflector formed from the conductive elements 1400. As a result,varying the impedance of the variable impedance junction elements 1504also varies the scattered electromagnetic signal scattered from thecombination conductive elements. In particular, the varying of theimpedance per unit lengths of the combination conductive element 1516varies the amplitude of the reflecting property of the reflector.

Referring now to FIG. 19, therein illustrated are plan views of a firstexemplary planar variable reflector 1600 and a second exemplary planarvariable reflector 1604 each having a plurality of interconnections 1500of conductive elements 1400.

The first planar variable reflector 1600 includes a plurality ofinterconnections 200 that are placed side-by-side. The interconnections1500 are spaced apart from one another by a distance 1608. For example,the distance 1608 of the spacing between the side-by-sideinterconnections 1500 is substantially greater than the width 1412 andheight 108 of the conductive elements 1400 of the interconnections 1500.Accordingly, the strength of electromagnetic fields being reflected orscattered in a direction perpendicular to the direction of the length1404 of the conductive elements 1400 is kept low. According to variousexemplary embodiments, the distance 1608 of the spacing can be adjustedto further vary the reflectivity of the first planar variable reflector1600. According to one exemplary embodiment, the distance 1608 of thespacing is selected to be approximately equal or greater than the length1404 of one of the conductive elements 1400 of the interconnections1500.

The elongated conductive elements 1400 forming the interconnections 1500of the first exemplary planar variable reflector 1600 are oriented in anx-axis direction 1612. For example, the elongated conductive elements1400 are parallel to one another. The conductive elements 1400 andjunction elements 1504 are supported by a support layer 1616. Theconductive elements 1400 are positioned to cover a two-dimensional areaof the surface of the support layer 1616. According to various exemplaryembodiments, the support layer 1616 can be permeable to electromagneticfield. For example, the support layer 1616 is formed of a dielectricsheet or similar support structure. For example, the support layer 1616is a dielectric material having a low dielectric permittivity. Forexample, the permittivity of the dielectric support layer 1616 isapproximately equal to the permittivity of air. For example, the supportlayer 1616 is selected to be a thin layer.

A plurality of parallel combination conductive elements can be formedfrom the elongated conductive elements 1400 through the control of thejunction elements 1504. It will be appreciated that according to variousexemplary embodiments described herein, the length and/or the impedance(including impedance per unit length) of the combination conductiveelements can be adjusted through control of the junction elements 1504.

Since the plurality of conductive elements cover a two-dimensional area,the combination conductive elements formed therefrom will also cover thetwo-dimensional area. Incident electromagnetic signal reaching the areawill energize the combination conductive elements further creatingscattered (reflected) electromagnetic signals. Accordingly, theplurality of conductive elements 1400 covering the support layer 316acts a variable electromagnetic field reflecting surface.

Since each of the conductive elements 1400 are oriented in the x-axisdirection 1612, combination conductive elements formed therefrom will beresponsive to the directional components of incident electromagneticsignals that are aligned with the orientation of the conductive elements1400 of the first planar variable reflector 1600. Accordingly,interconnections 1500 of conductive elements 1400 forms a directionalreflector, herein referred to as a x-planar reflector 300. It will beappreciated that the x-planar reflector 300 can be used to isolate andreflect components of incident electromagnetic signals having anorientation or polarization that is aligned with x-axis direction 312.

Similarly, the second planar variable reflector 304 includes a pluralityof interconnections 200 that are placed side by side. Theinterconnections 200 are spaced apart from one another by a distance324.

For example, the distance 324 of the spacing between the side-by-sideinterconnections 200 of second planar variable reflector 304 issubstantially greater than the width 112 and height 108 of theconductive elements 1400 of the interconnections 200. Accordingly, thestrength of electromagnetic fields being reflected or scattered in adirection perpendicular to the direction of the length 104 of theconductive elements 1400 is kept low. According to various exemplaryembodiments, the distance 324 of the spacing can be adjusted to furthervary the reflectivity of the first planar variable reflector 300.According to one exemplary embodiment, the distance 324 of the spacingis selected to be approximately equal or greater than the length 104 ofone of the conductive elements 1400 of the interconnections 200.

The elongated conductive elements 1400 forming the interconnections 200of the second exemplary planar variable 304 are oriented in a y-axisdirection 328. For example, the elongated conductive elements 1400 areparallel to one another. The conductive elements 1400 and junctionelements 1504 are supported by a second support layer 332. Theconductive elements 1400 are positioned to cover a two-dimensional areaof the surface of the second support layer 332. According to variousexemplary embodiments, the support layer 332 can be permeable toelectromagnetic field. For example, the second support layer 332 isformed of a thin dielectric sheet or similar support structure. Forexample, the second support layer 332 is a dielectric material having alow dielectric permittivity. For example, the permittivity of thedielectric support layer 332 is approximately equal to the permittivityof air. For example, the support layer 332 is selected to be a thinlayer. A plurality of parallel combination conductive elements can beformed from the elongated conductive elements 1400 through the controlof the junction elements 1504. It will be appreciated that according tovarious exemplary embodiments described herein, the length and/or theimpedance (including impedance per unit length) of the combinationconductive elements can be adjusted through control of the junctionelements 1504.

Since the plurality of conductive elements cover a two-dimensional area,the combination conductive elements formed therefrom will also cover thetwo-dimensional area. Incident electromagnetic signal reaching the areawill energize the combination conductive elements further creatingscattered (reflected) electromagnetic signals. Accordingly, theplurality of conductive elements 1400 covering the support layer 332acts a variable reflecting surface for electromagnetic signals.

Since each of the conductive elements 1400 are oriented in the y-axisdirection 328, combination conductive elements formed therefrom will beresponsive to directional components of incident electromagnetic signalsthat are aligned with the orientation of the conductive elements 1400 ofthe second planar variable reflector 1604. Accordingly, interconnections1500 of conductive elements 1400 forms a directional reflector, hereinreferred to as a y-planar reflector 1604. It will be appreciated thatthe y-planar reflector 1604 can be used to isolate and reflect incidentelectromagnetic signals having an orientation or polarization that isaligned with y-axis direction 1628.

Referring now to FIG. 20, therein illustrated is an exemplarymulti-directional variable reflector 1700 formed by stacking a pluralityof support layers 1616, 1632 having directionally oriented conductiveelements 1400. As shown in FIG. 9, the y-planar reflector 1604 ispositioned over the x-planar reflector 1600 such that the reflectingareas of the two reflectors 1600, 1604 are coincident. This coincidencecan be seen from the corresponding positioning of conductive elements1400 of the x-planar reflector 1600 with the conductive elements 1400 ofthe y-planar reflector 1604. The supporting layer 1632 of the y-planarreflector 1604 is permeable to electromagnetic signals. Accordingly,some of the incident electromagnetic signals reaching the y-planarreflector 1604 permeate through the supporting layer 1632 to reach thex-planar reflector 1600.

In addition to varying the length and the impedance of the combinationconducting elements 1500 that act as reflecting elements, themulti-directional variable reflector 1700 is further operable toselectively vary a direction-dependent reflecting property of thereflector 1700 based on the control of the variable impedance junctionelements 1504. For example, the reflector 1700 can be adjusted toselectively reflect directional components of incident electromagneticsignals aligned with only the x-axis direction 1612, only the y-axisdirection 1628, or both directions.

For example, to adjust the multi-directional variable reflector 1700 toonly reflect directional components of incident electromagnetic signalsin the y-axis direction 1628, the variable impedance junction elements1504 of the second support layer 1632 are controlled to have a highimpedance such that the combination conducting elements formed from theconducting elements 1400 of the second support layer 1632 will have ahigh impedance per length. As a result, when y-axis direction orientedcombination conducting elements of the second support layer 1632 areenergized by the y-axis direction component of incident electromagneticsignals; the resulting current flow in the combination conductiveelements will be low. Consequently, the scattered (reflected)electromagnetic signals from these combination conductive elements willalso be low. By contrast, the junction elements 1504 of the firstsupport layer 1616 are controlled to have lower impedance such that thecombination conducting elements formed from the conducting elements 1400of the first support layer 1616 will have lower impedance per length. Asa result, when x-axis direction oriented combination conducting elementsof the first support layer 1616 are energized by x-axis directioncomponents of the incident electromagnetic signals; the resultingcurrent flow in the combination conductive elements will be higher.Consequently, the scattered (reflected) electromagnetic signals from thecombination conductive elements of the x-planar reflector 1604 will behigh. Therefore the scattered electromagnetic signals emitted from themulti-direction variable reflector 700 will be due primarily to theenergizing by the x-axis direction component of the incidentelectromagnetic signal. Measuring the scattered electromagnetic signalswill allow a determination of properties of the x-axis component of theincident electromagnetic signals. It will be appreciated that themulti-directional variable reflector 1700 allows for determination ofdirection-dependent properties of the incident electromagnetic signaland/or space surrounding the reflector 1700. Furthermore, examining thescattered fields at a distance will provide an indication of one or moreproperties of the environment near the multi-directional variablereflector 1700 through which the waves having a given field orientationor polarization traveled because only waves with the given orientationor polarization impinging on the reflector 1700 will create a measurableresponse.

It will be understood that the multi-directional variable reflector 1700is shown to have the y-planar reflector 1604 stacked above the x-planarreflector 1600 by way of example only and that various othercombinations are possible. According to various exemplary embodiments,the x-planar reflector 1600 can be the top reflector and is stackedabove the y-planar reflector 1604. According to various exemplaryembodiments, the multi-directional variable reflector 1700 can be formedof more than two support layers having conductive elements supportedthereon. For example, in addition to the x-planar reflector 1600 andy-planar reflector 1604, additional reflectors having conductiveelements oriented in other directions may be added to the stackedreflectors.

Referring now to FIG. 21, therein illustrated is a perspective viewaccording to various exemplary embodiments of a mechanically poweredvariable reflector 2000. A supporting layer 2004 having a pluralityelongated conductive elements of the reflector 2000 is coupled to amotor 2008. For example, the variable reflector 2000 can be coupled tothe motor via a shaft 2012. A plurality of elongated conductive elements1400 and variable impedance junction elements 1504 are supported on thesupporting layer 2004. For example, the elongated conductive elements1400 and junction elements 1504 can be oriented in a similar manner tox-planar reflector 1600 or y-planar reflector 1604. With this embodimentboth mechanical rotation and change in the connection between conductingelements can both be used to create the modified reflectivity eithersimultaneously or independently. A simple rotating object with elongatedmetal elements can be used to provide a very simple modulated reflector.

Rotating the supporting layer 2004 to a first position causes theconductive elements 1400 to be oriented in a first direction and for thevariable reflector 2000 to isolate and reflect components of incidentelectromagnetic signals having an orientation or polarization that isaligned with the first direction. The supporting layer 2004 can berotated about the shaft 2012 by the motor 2008 to a second positionwherein the conductive elements 1400 are oriented in a second direction.In the second position, variable reflector 2000 isolates and reflectscomponents of incident electromagnetic signals having an orientation orpolarization that is aligned with the second direction. For example,rotating the supporting layer 2004 by an angle of 90 degrees causes thesecond direction to be orthogonal to the first direction. Throughrotation of the supporting layer 2004 the reflector 2000 can becontrolled to reflect different directional components of incidentelectromagnetic signals.

While exemplary embodiments described herein have linearly arrangedconductive elements positioned on a planar support layer, it will beunderstood that other arrangements of conductive elements are possible.According to one exemplary embodiment, the conducting elements arecurvilinear and are positioned on a curvilinear surface of a supportlayer.

According to one exemplary embodiment, electromagnetic simulation alongwith parameterization of the junction elements 1504 can be used toselect appropriate sizing and positioning of the conductive elements1400. In particular a systematic simulation of the response may beapplied. Furthermore, modern computers and numerical simulation toolsmay be used to allow the optimization of the various parameters.

For example, by defining a design outcome in terms of scatteredelectromagnetic field strength, polarization change, range offrequencies, a wide range of electromagnetic modeling can be used tocharacterize the scattering of the incident field as a function ofcharacteristics of the conductive elements 1400.

Iteratively adjustment of the parameters may be further carried out toachieve a desired response of the resulting reflector. For example, amanual succession of steps may include systematically adjusting themodel parameters to achieve a desired response. Alternatively anautomated process commonly referred to as inversion, whichsystematically modifies the model parameters with a goal of finding aset of parameters for the system that minimizes the difference betweenthe desired response and the model response, may also be applied.

Referring now to FIG. 22, therein illustrated is a schematic diagram ofa flowchart showing the steps of a method 2100 for adjusting theparameters of a reflector.

At step 2104, the desired attributes of the variable reflector isdefined. For example it can be defined that the variable reflectorshould be capable of reflecting electromagnetic signals in a specificfrequency range, of reflecting electromagnetic signals at a specificrange of amplitudes (amplitude of the reflecting property of thereflector) or of reflecting electromagnetic signals having specificorientation or polarization.

At step 2108, initial structural parameters of the variable reflectorare selected. For example, structural parameters can include one or moreof the size of a reflecting surface defined by the conductive elements1400, the spacing between interconnections 1500 of the reflectingsurface, the length of each conductive element 1400, and the type ofmaterial forming the dielectric substrate of the variable reflector.Furthermore, initial characteristics of the junctions 1504 can also beselected. The initially selected structural parameters of the variablereflector and initial characteristics of the junctions 1504 are definedas currently selected structural parameters and junction elementcharacteristics.

At step 2112, a simulation modeling of electromagnetic waves incident onthe variable reflector is performed using the selected structureparameters and junction characteristics as inputs. The simulatedscattered signal is outputted from the modeling.

At step 2116, the simulated scattered signal outputted from the modelingis translated into intermediate attributes of the variable reflector.For example, the intermediate attributes may be calculated based on acomparison of the input electromagnetic signals used in the simulationmodeling with the outputted simulated scattered signal.

At step 2120, the intermediate attributes of the variable reflector arecompared with the desired attributes of the variable reflector definedat step 2104.

At step 2124, it is determined based on the comparison of step 2120whether the intermediate attributes of the variable reflector areacceptable. For example, it is determined whether the values of theintermediate attributes are sufficiently close to the values of thedesired attributes of the variable reflector.

If at step 2124, the intermediate attributes are acceptable, thecurrently selected structural parameters and characteristics of thejunction elements are retained at step 2128. A physical variablereflector can then be manufactured according to the retained structuralparameters and junction element characteristics.

If at step 2124, the intermediate attributes are not acceptable, atleast one of the currently selected structural parameters or junctionelement characteristics is updated at step 2132. For example, theupdating may be based on an amount of difference between theintermediate attributes and the desired attributes of the variablereflector. For example, the updating of at least one of the selectedstructural parameters or junction element characteristics can use aperturbation approach known in the art. The updated structuralparameters and junction element characteristics are defined as thecurrently selected structural parameters and junction elementcharacteristics. The method returns to step 2112 to perform a furthersimulation modeling of electromagnetic waves incident on the variablereflector using the selected structure parameters and junctioncharacteristics as inputs.

Advantageously, various exemplary embodiments described herein applyscattering principle to create a variable wideband reflector where thereflecting property can be adjusted through systematic control ofjunction elements. Such variable reflectors can be used to measurevarious properties of signals or conditions.

For example, where properties of the conducting elements and thesurrounding space are known, measurement of the scatteredelectromagnetic field allows determination of properties of the incidentelectromagnetic signal. This can include frequency-related ororientation-related properties of the incident electromagnetic signal.

For example, where properties of the conducting elements and theincident electromagnetic signal are known, measurement of the scatteredelectromagnetic field allows determination of properties ofenvironmental conditions in the space surrounding the reflector. Forexample, in the case of junction elements having impedance that varieswith a changing environmental condition, measurement of the scatteredelectromagnetic field allows a determination of the impedance values ofthe junction elements, which provides a further indication of theenvironmental conditions. For example, where directional components ofthe incident electromagnetic signal are known, measurement of thescattered electromagnetic field allows a determination ofdirection-dependent properties of the environmental condition.

While the above description provides examples of the embodiments, itwill be appreciated that some features and/or functions of the describedembodiments are susceptible to modification without departing from thespirit and principles of operation of the described embodiments.Accordingly, what has been described above has been intended to beillustrative and non-limiting and it will be understood by personsskilled in the art that other variants and modifications may be madewithout departing from the scope of the invention as defined in theclaims appended hereto.

REFERENCES

-   1. Kraus, J. D., 1988, Antennas, McGraw Hill, ISBN 0-07-035422-7-   2. Aydin Babakhani, David B. Rutledge, and Ali Hajimiri, 2008,    Transmitter Architectures Based on Near-Field Direct Antenna    Modulation, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 43, NO. 12-   3. Brunfeldt, D. R., Ulaby, F. T., 1984 Active Reflector for Radar    Calibration Geoscience and Remote Sensing, IEEE Transactions on,    GE-22, Issue: 2-   4. Foster I. J., 1998, Modulating Reflector Circuit, U.S. Pat. No.    5,822,685-   5. Finkenzeller, K, 1999, RFID handbook: radio-frequency    identification fundamentals and applications, John Wiley (New York)    ISBN 0471988510-   6. Shober, R. A., Sweetman, E, Wright, G. A., 2001, Inexpensive    Modulated Backscatter Reflector, U.S. Pat. No. 6,243,012 B1-   7. Bracht, R., Miller, E. K., Kuckertz, T., 1997, Using an impedance    modulated reflector for passive communication, Antennas and    Propagation Society International Symposium, 1997, IEEE, 1997    Digest, v2

1. A system for measuring a material, the system comprising: at leastone transmitter for transmitting at least a first signal and a secondsignal; at least one variable reflector for reflecting a portion of thefirst signal at a first reflecting property to produce a first reflectedsignal, the portion of the first signal having traveled through thematerial, and for reflecting a portion of the second signal at a secondreflecting property to produce a second reflected signal, the portion ofthe second signal having traveled through the material; at least onereceiver for receiving at least a first received signal and at least asecond received signal, the first received signal comprising the firstreflected signal having traveled through the material and the secondreceived signal comprising the second reflected signal having traveledthrough the material, the first reflected signal and the secondreflected signal providing an indication of at least one property of thematerial.
 2. The system of claim 1, wherein the transmitting of thefirst signal and the second signal are temporally spaced apart.
 3. Thesystem of claim 2, wherein temporally spacing apart the transmitting ofthe first signal and the second signal permits independent observationof the first reflected signal and the second reflected signal
 4. Thematerial measurement system of claim 1, wherein the first signal andsecond signal are the same.
 5. The material measurement system of claim1, further comprising: a signal processor for isolating the firstreflected signal and the second reflected signal, the isolated reflectedsignals providing an indication of at least one property of thematerial.
 6. The material measurement system of claim 5, wherein thefirst received signal further comprises an unreflected portion of thefirst signal and the second received signal further comprises anunreflected portion of the second signal, and wherein calculating adifference between the first received signal and the second receivedsignal isolates the first reflected signal and the second reflectedsignal from the unreflected portion of the first signal and theunreflected portion of the second signal.
 7. The material measurementsystem of claim 1, wherein the first reflecting property is a firstreflectivity and the second reflecting property is a secondreflectivity.
 8. The material measurement system of claim 7, wherein atleast one property of the material comprises the permittivity of thematerial.
 9. The material measurement system of claim 7, wherein atleast one property of the material comprises the attenuation coefficientof the material.
 10. The material measurement system of claim 7, whereinthe first signal is a transient pulse and the second signal is atransient pulse and wherein a time delay between transmitting the firstsignal and the second signal and a corresponding pulse in the receivedfirst reflected signal and the received second reflected signal providesthe indication of at least one property of the material.
 11. Thematerial measurement system of claim 7, wherein the first signal is aperiodic signal and the second signal is a periodic signal having thesame period as the first signal, and wherein a phase delay between thefirst signal and the second signal and the received first reflectedsignal and the received second reflected signal provides the indicationof at least one property of the material.
 12. The material measurementsystem of claim 1, wherein the first reflecting property is a firstdirectional reflectivity to reflect signals having a first polarization,and the second reflecting property is a second directional reflectivityto reflect signals having a second polarization and wherein the at leastone property of the material comprises the anisotropy of the material.13. The material measurement system of claim 12, wherein the firstpolarization and the second polarization are orthogonal.
 14. Thematerial measurement system of claim 1, wherein the first signal has afirst polarization and the second signal has a second polarization, andwherein the at least one property of the material includes an anisotropyof the material.
 15. The measurement system of claim 14, wherein thefirst polarization and the second polarization are orthogonal.
 16. Thematerial measurement system of claim 13, wherein the first reflectingproperty and the second reflecting property are direction-independent.17. The material measurement system of claim 1, wherein the firstreflecting property is a reflectivity for a first frequency range andwherein the second reflecting property is a reflectivity for a secondfrequency range and wherein the at least one property of the materialcomprises frequency dependent properties of the material.
 18. Thematerial measurement system of claim 1, wherein the first signal has adifferentiable amplitude in a first frequency range and the secondsignal has a differentiable amplitude in a second frequency range, andwherein at least one property of the material includes frequencydependent properties of the material.
 19. The material measurementsystem of claim 1, further comprising a controller for selecting areflecting property of the variable reflector.
 20. The materialmeasurement system of claim 19, wherein the second signal is transmittedafter the first signal, and wherein the controller selects the firstreflecting property before the variable reflector reflects the portionof the first signal and the controller selects the second reflectingproperty before the variable reflector reflects the portion of thesecond signal.
 21. The material measurement system of claim 19, whereinthe transmitter sequentially transmits a plurality of signals; andwherein the variable reflector reflects a first subset of the pluralityof signals at a first reflecting property and reflects a second subsetof the plurality of signals at the second reflecting property; whereinthe controller adjusts the reflecting property of the variable reflectorduring the transmission of the plurality of signals.
 22. The materialmeasurement system of claim 21, wherein the controller adjusts thereflecting property of the variable reflector independently of thetiming of the sequential transmissions of the plurality of signals. 23.A method for measuring a material, the method comprising: transmittingat least a first signal into the material and a second signal into thematerial; controlling at least one reflector to reflect a portion of thefirst signal at a first reflecting property to produce a first reflectedsignal, the portion of the first signal having traveled through thematerial; controlling the at least one reflector to reflect a portion ofthe second signal at a second reflecting property to produce a secondreflected signal, the portion of the second signal having traveledthrough the material; receiving at least a first received signal and atleast a second received signal, the first received signal comprising thefirst reflected signal having traveled through the material and thesecond received signal comprising the second reflected signal havingtraveled through the material, the first reflected signal and the secondreflected signal providing an indication of at least one property of thematerial. 24.-65. (canceled)
 66. A variable reflector comprising: aplurality of elongated conductive elements interconnected by at leastone variable electrical impedance junction element, a variation of theimpedance of the junction element varying a scattering electromagneticfield scattering from the plurality of interconnected elongatedconductive elements when energized; wherein a first set of the pluralityof elongated conductive elements is interconnected by a first set of theat least one junction element and is supported on a firstelectromagnetically permeable support layer and has a first orientation;and wherein a second set of the plurality of elongated conductiveelements is interconnected by a second set of the at least one junctionelement and is supported on a second support layer and has a secondorientation that is different from the first orientation.
 67. Thevariable reflector of claim 66, wherein the first electromagneticallypermeable support layer is disposed on the second support layer.
 68. Thevariable reflector of claim 66 wherein the first orientation isperpendicular to the second orientation.
 69. The variable reflector ofclaim 66, wherein the scattering electromagnetic field is dependent onan amount of alignment of the incident electromagnetic signal with anorientation of at least one of the first set of elongated conductiveelements and the second set of elongated conductive elements.